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Psyche 5:171-180, 1888.

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MY RMECOPHILISM.
BY WILLIAM TRELEASE, ST. LOUIS, MO.
[Address of the retiring president of the Cambridge Entomological Club, 11 January 1889.1 It is customary in some circles for a
president's address to consist of a gener- al r4sum4 in some line of scientific work. I have availed myself of this opportunity to review the more important literature
on a branch of biological work which has long possessed an unusual degree of in-
terest for me,-namely, the mutual re-
lations, amounting in some cases to
symbiosis, existing between ants and cer- tain members of the vegetable kingdom.
Such a forced review is profitable to
the writer, and it may be of interest
to the body before which it is read ;
but it by no means follows that it has
scientific value, for each worker must
perforce go back to original sources for information needed in his own researches. Quite naturally, I have treated the sub- ject from a botanical standpoint, since, with the exception of certain acquired
habits, the specializations are chiefly
such as fit plants to profit by the visits of ants to their vegetative or fruiting
organs.
I. THE FUNCTIONS OF EXTRA-NUPTIAL
NECTAR-GLANDS.
The chief sorts of glands situated on
the surface of plants or opening supes-
ficially, are divided into colleters and nectar-glands, according as they secrete resinous, m~~cilaginous, or gummy sub-
stances in the one case, 01- sugary fluids in the other. The first are apparently
for the most part protective, in that they form a coating over young parts in the
bud, which prevents drying or other
injury ; or they prevent the access of un- bidden guests to the flowers or fruit, or deter vegetable feeders from making an
onslaught on the parts which bear them,
-in this respect resembling raphides,
alkaloids, volatile oils, etc., within the plant.* A few such structures serve for
the attachment of fruit or seed to animals for purposes of dissemination, etc. The
digestive glands of carnivorous plants
may, perhaps, be regarded as derived
from some of the numerous types of col-
leters, and the foliar nectar-glands of
many plants are pretty clearly homolo-
gous with the serration- and other col-
leters of the same and related species.
Typical colleters are, therefore, chiefly protective, and there is good reason for believing that many of them have been
evolved for preventing the access of ants to the flowers of plants, where, almost
without exception, the presence of these insects works mischief.
Nectar-glands, on the other hand, are
of indirect use by attracting suitable pol- * For a recent discussion of the protection of plants, especially from the attacks of snails, by col- leters and other deterrent structures, see an elaborate paper by Stahl in Jenaische Zeitschrift fir naturwiss. und medicin, xxii.--reprinted under the title "Pflan- Zen und schnecken," Jena, 1888.-Abst. in Bot. centralblatt, 1888, v. 36, p. 164-170.




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PSYCHE. [February-March iSSg.
linators to the flowers, by luring prey to the digestive apparatus of some carni-
vorous plants, or by maintaining upon
the plant a body-guard of pugnacious
insects, which more or less efficiently
protect it against certain of its enemies. Since the time of Sprengel (29).
it has been well known that many flow-
ers contain glands which secrete nectar
;is a source of attraction to insects able to cross-pollinate them. The occurrence
of this fluid was known long before his
day, but its use was either not investi- gated, or misunderstood. Indeed his
keen insight into its &son d'etre was
scarcely appreciated for three-quarters
of a century, until Mr. Darwin took the
subject in hand in his classical work on the pollination of orchids. To-day, how- ever, Sprengel's views, cleared and
somewhat broadened, and carried into a
thousand little details that he had not
followed out, are contested by very few
persons. . So far as our purpose is con- cerned, nothing further need be said of
floral nectar, since the structure and
habits of ants are such as to practically debar them from any important r61e in
pollination. In fact entomophilous
plants usually teem with devices for pre- venting their access to floral nectar,-
for which, very naturally, they have a
great liking'.
The relation of extra-floral nectar to
the fructification of plants was, I believe, first clearly pointed out by Delpino,
(6, 86), who coined the terms "nup-
tial" and "exti-a-nuptial" to indicate on the one hand that which attracts polli-
nators, and on the other, that which is
of no value in this respect. These
terms are much less objectionable than
"asexual" and "sexual," the former of
which has recently been used by Kny
(13) as synonymous with extra-nup-
tial. With nuptial nectar secreted out-
side the flower, we have quite as little to do tis with that secreted within it, for the reasons already indicated ; but the sub- ject of extra-nuptial nectar and its rela- tion to ants, is deserving of a much fuller discussion than can be given to it here
without going into details to a tiresome length.
Without an undue amount of search-
ing, I cannot say when 01- by whom it
was first observed that certain flowers
produce nectar outside of their flowers, but it has certainly been known for a
long time. Hall, a pupil of Linnaeus,
had seen the extra-floral glands of various plants ( I I, 266). Krunitz (I+), whose
work I know only from references
in Sprengel and elsewhere, observed
bees at the stipular nectaries of Vicia, over a century ago, and similar obser-
vations had undoubtedly been made, if
not heeded, even earlier. But the first
careful investigations into organs of this sort, and their secretions and uses, were made simultaneously but independently
by Delpino (6 and 7) in Italy, and Belt
(3), in tropical America. while
other observers have contributed many
isolated facts to the knowledge of these organs in the fifteen years since the ob- servations and conclusions of these nat- uralists were published, the task of
following up and systematizing the dis-
tribution of protective nectar has de-




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February-March iSSy.1
PSYCHE.
volved upon Delpino ( 8 ), whose
evidently thorough studies are now in
course of publication, the results already printed occupying over 150 quarto
pages.
Broadly speaking, this class of extra-
floral nectar-glands, by their secretion, attracts to the plants which bear them
hordes of ants (rarely wasps), which
constitute a temporary and changing
body guard, disputing the presence of
all other insects with the exception of
their proteges the sugar-excreting
aphides, coccids, etc., and resisting,
often furiously and effectively, the on- slaughts of ruminants and other large ani- mals. That this is a true explanation of the reason for the existence of these
structures, is generally admitted, today.* The plants which possess such glands
are phaenoganis and ferns, chiefly of the tropics and s~~btropics ; yet tlie number in our ow11 and other temperate floras
is rather sui-prisingly large.
The ants attracted by extra-nuptial
nectar are mainly the omnipresent, om-
nivorous species. Protection is often
afforded against various caterpillars and other leaf-eating larvae, as Ratzeburg
(24) and others have observed ; but
the body-guard appears primarily des-
--
* For a. general negation of the prevalent notions concerning nectaries of all sorts, coupled with a good histological study of many of these organs, reference should he made to Bonnier's essay- -Les Nectaires-in Annales des sci. nat., Bot., 1879, v. 8. alsopublished separately at Paris,-which reverts to the theories of the last century.
It is also to be observed that Kerner von Marilaun, the learned Viennese biologist, quite recently describes the petiolar glands of Popiilus as organs of absorption Pflanzenleben, v.1.215),- but without giving reasons for his belief nor an indication that another function had been previously ascribed to them.
tined to resist the depredations of other members of their own group,-the leaf-
cutting ants,-which swarm in tropical
and subtropical regions, and quickly
defoliate plants not provided with this
defence unless efficient service is ren- dered by colleters or alkaloids, which
prevent the access of these insects to im- mature and tender parts, or render these distasteful to them. Delpino was at first inclined to explain the occurrence of
protective nectar in regions where no
leaf-cutting ants are found, solely with reference to herbivorous larvae. But
it has been shown several times that
snch larvae are permitted in large num-
bers on plants provided with a body-
guard of ants attracted by nectar. I
have myself observed this in the case of Gassy$ium, which suffers notoriously
from the attacks of Aletia and He&-
this, although it is unusually well sup- plied with extra-nuptial nectar that at- tracts numerous ants which to a certain
but insufficient extent do attack tlie cat- erpillars of the moths named. The
same thing is also to be seen on Populus modifera in the west and south, where
this tree is subject to very disastrous at- tacks from the larvae of a chrysomelid
beetle, PZagiodera scripts, and a moth,
Acronycta å´po@Zi Careful observa-
tions of the behavior of insects attracted by extra-nuptial glands, carried through a number of seasons, and on plants with
differing surroundings, accompanied by
correct identification of the insects are possible to local entomologists every-
where, and are much to be desired.
There seems little reason to doubt




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174 p>s' 2"THE. [February-March 1889.
that these protective adaptations are the result of natural selection, acting through the ages of co-existence of plants and
their enemies.
I have long felt a con-
viction that the occurrence of extra-
nuptial nectar-glands on so many of our
own plants which are not menaced by
leaf-cutting ants (except in the extreme southwest), must date back to later
geological periods, characterized by a
warmer climate in northern latitudes,
and by a much greater prevalence of
ants of many kinds than is the case with us now* ; and that a corresponding prev- alence of leaf-cutting or other noxious
ants is demonstrable in these periods.
Unfortunately, I have never been able
to pursue the subject in this direction, but the immense collection of fossil ants in the possession of Mr. Scudder must
furnish instructive data for testing this opinion, when its treasures shall have
been sufficiently studied to show the
affinities of the prevalent genera of those times in northern America. That struc-
tures corresponding in position to the
foliar glands of existent species of Popu- Zas were found on tertiary plants, is
shown by their occurrence on P. glue-
dulz~era, Heer (3 I, p. 290), but I do
not now remember that they have been
recognized elsewhere.
While, as has been shown, the secre-
tion of food for protective ants is often rendered superfluous by the provision of other more direct deterrents, the two
classes of protective adaptation sometimes occur conjointly. Lundstrom (I 6, p.
* On this point see a very instructive note by Mr. Belt in Nature, 1877, v. 16, 122.
83) has shown that the leaves of Popu-
Zus which do not possess nectar-glands
are distinguished also by the thinness
and flexibility of their compressed peti- oles, by which caterpillars, etc. are to some extent rendered uncertain in their
footholds on these easily shaken leaves. Delpino and Schimper have also ob-
served the protection secured to Ricinits by its smooth and very glaucous stems,
though its leaves likewise bear extra-
nuptial glands.
An aberrant function of the nectar-
glands on the leaves of some pitcher
plants is that of luring to their destruc- tion, insects which are captured and di- gested or at least macerated by these
carnivorous plants. From the large
number of ants found in our Sarracenia
leaves in a state of nature, this would
seem to be true of species of this group ; for these ubiquitous insects are certainly led to the orifices of the pitchers by the sugary secretion on the exterior. In his latest paper (8, 227), Delpino holds this secretion to be protective; as in the
cases already passed in review ; but the opinion which I have here and elsewhere
(30, 328) expressed, is that of Riley (25, p. 25), Mellichainp (18, I ~g), Gray
( 10, I I 2) , and others, some of them
early writers on Sarraceniaceae. That
ants are largely victimized by these
plants does not, of course, signify that the structure of the latter is not such as to facilitate the capture of larger, flying insects, which are, in fact, often found entrapped, especially by the southern
Sarracenias and the Californian Dar-
Zingto n iu .




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February-March 1SS9. J PSYCHE. 175
Leave cannot be taken of the extra-
nuptial nectar of phaenogams and ferns
without reference to the sugary exudation which escapes on the emission of sper-
matia of Urediweae. As was shown by
RAthay (23), this is greedily devoured by ants and other honey-loving insects. But the sesvice that these render, if any is rendered, is not clear, 4nce it is not cer- tain whether the spermatia are spores or male reproductive cells, though there is reason for considering t I1 em to be spores.* That ants play a considerable part in scat- tering these bodies is a necessary a priori conclusion ; but it is not so evident how far the secretion of a sugary fluid is to be regarded as an adaptation to this end.
It has recently been explained by Lud-
wig (I 5) in accordance with the Del-
pino-Belt theory.
Some part of a plant is not infre-
quently tenanted by ants which find
there shelter or food to their liking, but so far as our own and other temperate
floras are concerned, there appears to
be no adaptation by which the plant is
fitted to maintain or especially profit by this residence of ants. The heart-wood
of some of our forest trees is often in- habited in this manner by the large
black ant, Formica$emsyZvanica. On
several occasions I have also found an
undetermined small brown ant nesting
in the old hypanthia of Calycanthus,
still adhering to the 'plant, in the botanic * See Plowright, managr. of British Uredineae and Ustilagineae, 1889, 11 et seq.
garden at St. Louis. No doubt any
close observer of the ways of ants can
add many instances of the same general
character, in which, so far as the biol- ogy of the plant is concerned, the ants
are merely accidental residents, though
their pugnacity may lead them to resist
the attacks of other creatures whose
presence is distasteful to them.
It is also known that
ants sometimes
construct somewhat elaborate nests on
plants. Some cases of this sort are
noted by Westwood (34, 222) and Pack-
ard (21, 317), and I presume that a
person more familiar than myself with
entomological literature could cite other references on this subject. Several years ago I contributed to the Club the gist
of observations on a colony of Crema-
toyaster which had erected a nest
over their wards, certain aphides, on a
branch of Andromee where they ap-
parently spent their entire time (Psyche, v. 3, 31). Similar nests had been ob-
served before by others psyche,^. 3,343 ;& and the Minutes of the meetings held dur- ing 1883, 2). In the case observed by my- self the ants appeared to be kept at their post by the aphides (which they may
themselves have placed upon the plant),
and the shelter was evidently constructed as much for these insects as for theim-
selves. Where ants protect the enemies
of a plant in this manner, they are clearly injurious to it in the first place, though they may at the same time keep off others of its enemies in endeavoring to guard
their prot4g6s. The good may even
more than counterbalance the harm done,
and L~mdstr6m has suggested that in




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[February-March 1889.
some cases aphides may be held as serv-
ing their host-plants in the capacity of wandering nectaries (16, 84). It is
certain that they are sometimes a stronger source of attraction to ants than either nuptial or extra-nuptial glands.
3. MYRMECOPHILOUS PLANTS,
PROPER.
Some of the earlier travellers, in de-
scribing their collections, make mention of the fact that cavities in the stems
and
stipules, or pockets on the leaves, of
some tropical plants are tenanted by
ants. This was recorded for Cecropia
as early as I 648 by Marcgi-avius (I 7), and for Acacia in 1651, by Hernan-
dez ( I 2) . Though scattering observa-
tions of more or less biological interest occur in the literature of the succeeding 225 years, it was not until the early part of the last decade that these plants re- ceived careful study. In 1872 Professor
Cai-uel published a short paper (3)
on species of Hydno$hytum and
Mj~vzecodia, two 1-ubiaceous genera
that had been known to harbor ants at
least since the studies of Rumpf in I 750. The field notes and material for this
paper were obtainecl from Beccai-i, who
was led to believe that shortly after ges- mination the bases of these plants are
pierced by ants (subsequently identified as species of Crematogaster and fi-
domyrmex) which tunnel the gall-like
enlargement in various directions, mak-
ing a permanent residence there. The
plants were even thought to die while
quite small if not pierced, though these attacks might have appeared necessarily
injurious, to another observer. Later
observations by Forbes (9) and es-
pecially by Treub (33) who has
made good use of the unusual facilities
afforded by the botanical garden at
Buitenzorg in Java for cultivating tropi- cal plants, seem to show that this punct- uring of the stem is not so essential to the life of the plant as was supposed by
Beccari ; for in a series of cultures it was found that not only do young plants and
seedlings develop when removed from
all possibility of ant visits, but the exca- vations and perforations in their stems
appear spontaneously. According to
Treub, these elaborate structures, which in a state of nature appear to constantly serve as domiciles for ants, represent in reality a highly developed water-tissue, by which the plant is adapted to its
epiphytic habit. The view that they
are not primarily connected with the
maintainance of a body-guard of ants, is accepted by Schumann (28,419) in the
last extensive study of n~yrmecophilous