HAIRS ETC . 
114 
of animals and subsequently germinate. The tubers of Senecio articulata 
may be rolled along the ground by the wind, like the plants of Sela- 
ginella lepidophylla . The bulbils that are so frequent in inflorescences 
may be jerked to a distance when the plant is shaken. In reproduction 
by suckers, runners, or similar methods, the length of these is usually 
sufficient to ensure separation. 
Appendix. Hairs, Emergences, Latex, &c. A 
few minor anatomical features remain to be mentioned, as 
they are of importance in classification, natural history, &c. 
Hairs are cellular outgrowths from the epidermal tissue, branched 
or unbranched, of the most various*shapes, and are exceedingly common 
on all parts of plants (for descriptive terms see p. 53). Their use is 
often doubtful. The dense hairy covering of many xerophytes checks 
transpiration, the stinging hairs of Urticaceae, Loasaceae, &c. are pro- 
tective, the barbed hairs of the fruits of Galium, Blumenbachia, & c. serve 
for animal distribution, and so on. 
Emergences are outgrowths of the surface which arise from other 
tissues as well as the epidermis, e.g. the tentacles of Drosera, which 
contain vascular bundles, the prickles of Rosa and Ribes, and other 
such outgrowths. 
Latex is a milky fluid, usually white or yellow, contained in special 
laticiferous vessels or cells which run through the tissues of certain plants, 
e.g. Euphorbia, Cichorieae (Compositae), many Papaveraceae, Apocyna- 
ceae, Asclepiadaceae, Sapotaceae, &c. The fluid contains substances 
of various kinds ; some are of use in the nutrition of the plant, and to 
some extent the laticiferous tissue therefore replaces the phloem ; others, 
e.g. caoutchouc, are apparently excretory products of little or no use to 
the plant. 
Raphides are needle-shaped crystals of calcium oxalate, contained in 
the cells, especially in young growing parts and in Monocotyledons. The 
painful effects of chewing a piece of the leaf of Arum maculatum are 
due to the raphides sticking into the mucous membrane. 
Water-pores or hydathodes are openings, resembling stomata, upon 
leaves or elsewhere, through which the plant excretes water, often con- 
taining other substances, e.g. chalk, in solution. During the day evapo- 
ration carries off the water, but at night it often accumulates and is 
generally mistaken for dew. The drops of water so commonly seen in 
the morning on the tips of grass blades have been thus formed. Water- 
pores are also found in many species of Saxifraga, Tropaeolum, Fuchsia, 
Caladium, &c. When the water contains sugar in solution, a nectary 
(p. 88) is formed 1 . These are usually in flowers, but there are many 
cases of extra-floral nectaries, e.g. on the leaves of the cherry-laurel 
(Prunus), stipules of Vicia, Viola, &c. Extra-floral nectaries usually 
attract ants in large numbers, and this brings to the plant a certain 
advantage by keeping off caterpillars, &c. Several tropical plants show 
extreme cases of adaptation in this direction, by housing and feeding 
1 Usually there is no pore in a nectary, the fluid being excreted by 
the superficial cells. 
