66 LEAVES. 
support themselves, as the Pea, the Vine, the Vetch, &c. 
They wind spirally round neighbouring bodies, and thus 
support the plant. 
230. They are supposed to be abortive petioles, pedun- 
cles, or branches ;—petioles in the Pea and the Vetch, pe- 
duncles or racemes in the Vine. In.some species of Smilax 
they are considered abortive stipules. as 
231. Sprnes or Thorns. Sharp-pointed organs, which 
arise from the woody or internal part of the vegetable. 
They are supposed to be abortive buds, as in the Sloe-tree, 
the thorns of which are converted into branches, if it 
transplanted to a rich soil. - 
232. Pricxizs (Aculei) arise from the bark only, and can 
be easily detached, asin Rose, Bramble, &c. : 
233. Gianxps, minute globular bodies observed in many 
parts of the plant, as at the base of the sexual organs m the 
Cruciferz, destined to secrete a particular juice from the ge 
neral mass of fluids. This name is also applied to the recep- 
tacles filled with essential oil in many parts of the 4 
tiacew, and particularly in the leaves of the Myrtacee a 
2 Labiate. These are called vesicular glands, and may 
' easily seen in the leaves of the Myrtle and of the Orange, 
giving them a dotted appearance. The Ice-plant (Mesem- 
bryanthemum erystallinum) takes its name from the number 
_ of glands on its surface, filled with a clear, colourless, trans- 
parent liquid. ‘ 
234. Hats are found chiefly on plants which grow in dry 
situations, and in these cases it is thought that they enlarge 
the absorbing surface: they are then termed Lymphatic. 
They are not found on very succulent or on aquatic plant 
growing where there are abundant supplies of moisture. 
many plants the hairs are the excretory ducts of glands, 
_ inthe Nettle (Urtica), the hairs of which irritate the sk 
_ When very thickly set, they protect from the effects 
"great heat or cold, asin the Great Mullein, 
