6 
NATURE 
[AZay 6, 1886 
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 tapering, 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 extraordinary size. But the ordinary 
elevation of this tree is 25 to 50 feet, with a circumfer- 
ence of 12 to 20 feet. The leaves, when young and in 
vigorous growth, attain a breadth of 12 to 15 inches, and 
are ofa 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 tra- 
veller.” An Indian species (Urézca or Laportea 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 as 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. Urttca wrentissiéma, a Timor species, 
which is known to the natives by the significant appella- 
tion 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. J/alpighia urens bears on its leaves 
hairs 14 inch long, which are pressed flat along the surface. 
These act very similarly to those of Urtica. 
The Loasez, 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 chemi- 
cally 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 harmless in effect, but very un- 
pleasant to its assailant. Thus very many of the Sola- 
naceous plants have poisonous fruit, as 4 tropa Belladonna, 
and some species of Solanum. The whole plant is charged 
with juice of great pumgency in many of the Ranuncu- 
laceee, R. sce/eratus causing sores if allowed to come into 
contact with a delicate mucous membrane such as that of 
the mouth. Parts of the Aconite (4. Mafel/us) are in- 
tensely poisonous, while the seeds of S¢tychnos Nux- 
vomica yield the well-known drug strychnine. Others 
have a latex or juice which is intensely bitter and un- 
pleasant 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 Cruciferae, as the mustard and the 
radish. The aromatic Umbelliferze, also, are protected in 
this way from many of their enemies, the peculiar flavour 
which they possess being very unpalatable to many birds 
which are attracted by theirfruits. 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-fertilisa- 
| tion of the plants. 
Such are Arum Dracunculus and 
Stapelia, a genus of Asclepiadacez. . 
A very different kind of defence against intruders is 
foundin a Sumatran parasite, Hydriophytum formicarum. 
This plant, instead of developing special weapons of its 
own, attracts to itself a colony of ants whose sting is very 
severe. These resent very effectually the attacks of ani- 
mals inimical to the plant. It is described as parasitic on 
trees in 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 spherocephala, 
but a more elaborate one, as the plant not only serves 
as a habitation for the ants, but develops certain organs 
to attract them to it. The stem and branches are fur- 
nished 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, the 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, con- 
sisting of delicate masses of cells containing an oily 
secretion. Cecrofza is also 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 
Polygonaceee (77iplaris Schomburghkiana), 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 orchis (Schomburghkia tibicinis), 
which, he says, has pseudo-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 the former is to secure the due trans- 
ference of the latter from the stamen of one flower to the 
pistil of another, and this is effected in most cases by 
some particular insect. The invasion of others would 
hence lead to loss of honey or pollen, or both, with- 
out securing the end aimed at. It is natural, there- 
fore, 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 the ground, and many and various are the pitfalls 
-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 cups, which are filled with 
water, thus presenting 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 Polygonacee. 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. Sz/ewe, the catchfly, and Cz7cea, the 
enchanter’s nightshade, also are examples of plants fur- 
nished with sticky glands. Lacfuca, the wild lettuce, emits 
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