* 448 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
[ June 3, 1883. 
are three : the succulent leaves and shoots or the attractive fruits are 
assailed by animals in search of food ; the honey secreted by the flower 
to allure to it the particular insect adapted to bring about properly the 
process of fertilisation attracts also other insects whose presence is useless 
for such purpose, and which therefore are only robbers ; while the 
fertilising pollen is itself the object of desire on the part of others which 
are equally unable to apply it to ite legitimate purpose. 
The protective mechanisms of plants, therefore, so far as they are 
directed against aggressive animals, are to be looked for mainly in the 
neighbourhood of the young growing parts or the reproductive organs. 
Not exclusively, however, but generally the older vegetative parts are 
defended by their own inherent qualities, such as their hardness or 
wiriness, which keep them from being suitable for the food of their 
assailants. Such youug growing parts in many plants, particularly those 
growing in exposed regions, are plentifully supplied with thorns, spines, 
or prickles, rendering them in many cases extremely formidable. The 
thorns or prickles may be produced on almost all the vegetative organs, 
and may be merely epidermal structures, or much stronger in composition, 
containing considerable developments of woody tissue. These thorny 
plants are most noteworthy in desert countries, some that are met with 
there, notably the so-called ‘‘ Wait-a-bit ” Thorn of Africa, having spines 
of immense length, and being quite impenetrable by man or beast. Cases 
are not of infrequent occurrence where even the lion himself is a con¬ 
siderable sufferer by coming into collision with this plant. So great is the 
development of the thorny character in this region that Grisebach con¬ 
nects it particularly with desert exposure and scarcity of vegetation. 
Nor are thorny plants by any means c mfiued to such regions —on our own 
heaths the Gorse is a familiar plant, and one sufficiently formidable to 
passers-by; while other spiny Leguminosae, as the Reit-harrow (Ononis 
epinosa), are not infrequent by the wayside. A further peculiarity may 
be noted in connection with these plants; often the thorns do not occur 
above the point which is assailable by the animal in its search for foid; 
while, when the shoot has outlived its period of succulent condition, and 
its tissues have become hard and dry, the thorns do not persist, being 
much more numerous when the part is young. 
Nor is this spiny habit confined to shrubs or trees. The Cactuses, 
which are so remarkable a feature of the vegetation of America, are 
equally well protected. Their surfaces show great variety of development 
in this particular: some have small groups of thick rigid spines, others 
long flexible needles of intense sharpness, penetrating easily the skin of 
the assailant, and almost impossible to extract. 
More formidable defences even than thorns or prickles are found in 
the varieties of stinging hairs borne so plentifully on the leaves of many 
plants. These are represented in England by the two species of Stinging 
Nettle, which are, as everyone knows, capable of producing considerable 
discomfort to the unwary person who handles them. These are, however, 
not worth mentioning by the side of many of their tropical relations. 
The structure of the hair in all these is similar : a mass of cells forms a 
kind of swollen cushion below ; on this is seated the long tapeiing hair, 
which ends in a somewhat recurved point or hook. The walls of the 
upper part of the hair are very strongly silicified, and are, consequently, 
easily ruptured. Lower down there is but little silica. When touched 
or rubbed by the hand, the pressure drives the hair downward; at the 
eame time the brittle hook penetrates the skin and breaks off. The down¬ 
ward pressure forces out from rhe broken hair a fluid of intensely acrid 
nature, which, on entering the wound made by the point, sets up more or 
less severe inflammation. The fluid is generally conjectured to be formic 
acid—a view based on the fact that this acid can be obtained from the 
Nettle plant by suitable means. 
While the English representatives of this group of plants are 
sufficiently formidable to careless intruders, some of their connections in 
other parts of the globe are distinctly dangerous. A traveller in 
Australia describes a specimen of Urtica gigas in the following terms :— 
“ A specimen seen by Sir W. McArthur, still in full vigour, rises from its 
base by a series of buttresses of singularly regular outline, gradually 
tapeiing, without a branch, to a height of 120 to 140 feet. The trunk 
then divides into a regularly formed, wide-spreading head, which excites 
admiration from its extra -rdinary size. But the ordinary elevation of this 
tree is 25 to 50 feet, with a circumference of 12 to 20 feet. The leases, 
when young and in vigorous growth, attain a breadth of 12 to 15 inches, 
.and are of a beautiful dark-green colour. As may be expected, the 
poisonous fluid secreted from the foliage is very powerful, particularly in 
the younger leaves, and their sting is exceedingly virulent, producing 
.great suffering, not unattended with danger. It is found in the northern 
part of New South Wales, and is a great impediment to the traveller.” 
An Indian species (Urtica or Laponea crenulata) is equally obnoxious. 
It has rather large leaves, round which numerous small stinging hairs are 
placed. At certain seasons it emits when bruised so irritating an aroma 
ns to cause a copious flow of saliva and mucus from the nose and eyes for 
many hours, while violent fevers have been caused by the fluid poured out 
from its ruptured hairs. Urtica ureatissima, a Timor species, which is 
known to the natives by the significant appellation of “ devil’s leaf,” has 
been known to produce effects so violent as to last twelve months, and 
has in some cases even caused death. Malpighia urens bears on its 
leaves hairs 1 i inch long, which are pressed flat along the surface. These 
act very similarly to those of Urtica. 
The Loascm, or Chili Nettles, exhibit similar defences, their power of 
stinging being very severe. 
Other plants are protected also by hairs, which play rather a 
mechanical than a chemical part. Such are various species of Deutzia, 
particularly D. scabra, which bears on its leaves numerous star-shaped 
hairs whose walls are permeated with silica. 
Besides these defences, which are chiefly mechanical, though in the 
case of the Nettle a secretion acting chemically plays an important part 
in their behaviour, many plants are protected by chemical means alone. 
This is seen chiefly, though by no means exclusively, in the case of 
flowers and fruit. The plant secretes in different parts, or it may be 
throughout its system, a juice which may be poisonous, or acrid, or harm¬ 
less in effect, but very unpleasant to its assailant. Thu9 very many of the 
Solanaceous plants have poisonous fruit, a9 Atropa Belladonna, and some 
species of Solanum. The whole plant is charged with juice of great 
pungency in many of the Ranunculaceae, R. sceleratus causing sores if 
allowed to come into contact with a delicate mucuous membrane such as 
that of the mouth. Parts of the Aconite (A. Napellus) are intensely 
poisonous, while the seeds of Strychnos Nux-vomica yield the well-known 
drug strychnine. Others have a latex or j lice which is intensely bitter 
and unpleasant to the taste, as the different species of Spurge (Euphorbia), 
the Dandelion, the wild Lettuce, different species of Poppy, and many 
others. An acrid juice is to be met with in many Crucifer®, as the Mustard 
and the Radish. The aromatic Umbelliferse, also, are protected in this 
way from many of their enemies, the peculiar flavour which they possess 
being very unpalatable t o many birds which are attracted by their fruits. 
Other plants pour out resinous and other sticky secretions which serve the 
same purpose. Some others are protected by the possession of a very 
foetid odour, much resembling putrefying animal matter, though this has 
probably been developed to attract the carrion-loving flies which secure 
cross-fertilisation of the plants. Such are Arum Dracunculus and 
Stapelia, the latter a genus of Asclepiadacem. 
A very different kind of defence against intruders is found in a Suma¬ 
tran parasite, Hydriophytum formioarum. This plant, instead of develop¬ 
ing special weapons of its own, attracts to itself a colony of ants whose 
sting is very severe. These resent very effectually the attacks of animals 
inimical to the plant. It is dsscribed as parasitic on trees iu the form of 
a large irregular tuber, fastening itself to them by fibrous roots, and 
throwing out several branches above. The tuber is generally inhabited 
by ants, and is hollowed out by them into numerous winding passages, 
which frequently extend a good way along the branches also, giving them 
the appearance of being fistular. A similar arrangement is found in 
Acacia sphserocephala, but a more elaborate one, as the plant not only 
serves as a habitation for the ants, but developes certain organs to attract 
them to it. The stem and branches are furnished with very large thorns, 
which are set along them in pairs. The thorns are enormously swollen 
at their bases, which are hollow, and in these swellings the nests of the 
ants are found, tbe magnitude of the enlargement being no doubt caused 
by the irritation of the insects. At the base of each pair of thorns, about 
midway between the two, is found a large nectar-secreting gland, which is 
very active. The leaves of the plant are pinnate, and on the leaflets are 
numerous small pear-shaped glands, consisting of delicate masses of cells 
containing an oily secretion. Cecropia is als > protected in the same way ; 
its stem is hollow and contains the nests of the ants. As in the case of 
the Acacia, glandular structures are present, which attract the ants and 
afford them food. Schomburgk describes a plant belonging to the order 
Polygonacese (Triplaris Schomburgkiana), a native of Guiana, as having 
its trunk and branches hollow between the nodes, and serving as the 
habitation of venomous ants. He also mentions an Orchid (S ihomburgkia 
tibicmis), which, he says, has pseulo-bulbs arising from creeping root¬ 
stocks. These have a small hole at their base, and ants and other insects 
construct their nests therein. 
Turning more especially to the reproductive organs of plants, we find 
them attractive to intruders, not only on account of their own palatability 
or succulence, but as providing two especial delicacies much sought after 
by the insect world—honey or nectar, and pollen. The object of the 
secretion of tbe former is to secure the due transference of the latter from 
the stamen of one flower to the pistil of another, and this is effe ted in 
most cases by some particular insect. The invasion of others would hence 
lead to lorS of honey or pollen, or both, without securing the end aimed 
at. It is natural, therefore, to expect to find many contrivances to secure 
the secretion to the appropriate insect, and an almost infinite variety is 
found, some mechanical, others chemical, others partaking of the nature 
of both. The enemies most guarded against are those insects which we 
have seen in some other plants especially courted—ants. In assailing 
the plant they must usually ascend the stem from tbe ground, and many 
and various are the p’tfalls placed in their way. In the Teasle, the leaves, 
arranged in pairs along the stem, have their bases attached to it and to 
one another, forming deep cup9, which are filled with water, thus pre¬ 
senting an obstacle to their ascent. The leaves of the Pine Apple are 
arranged to bring about the same result. Some plants are surrounded in 
their growth by water, as many of the Polygonacete. In P. amphibium, 
which grows sometimes in water and sometimes on land, and has two 
characteristic forms accordingly, the land form has developed round the 
flower-stalks a number of sticky glands, while the water form has nothing 
of the sort. The two forms are protected from the ants, but by different 
means. Silene, the Catchfly, and Circsea, the Enchanter’s Nightshade, also 
are examples of plants furnished with sticky glands. Lactuca, the wild 
Lettuce, emits a milky juice on being assailed by them. Other plants, as 
some varieties of the Willow, have very slippery flower-stalks, which the 
ants cannot pass along. The forms of the flower, too, lend tcemselves^ to 
protective purposes : thus Antirrhinum and Linaria have a close-shuttmg 
corolla, which they cannot enter; Cobcea is furnished with free hairs 
growing on the corolla, which block the way to the nectar, and which are 
\ insurmountable by the insects. Where such means are not found, in some 
