GERMINATION. 153 



which facilitate their dispersion by the wind. These 

 tufts grow from the testa of the seed, and are not to be 

 confounded with the pappus of the Thistle, Dandelion, 

 <fec.; the latter, it will be remembered, is an outgrowth 

 of the calyx. 



252. The embryo, as already explained, generally 

 consists of an axis or stem called the radicle (or, more 

 properly, the caulicle, because it is in all respects a true 

 stem and not a root), and one or more leaves called 

 cotyledons, with sometimes, also, a bud known as the 

 plumule. As to the number of cotyledons, it may be 

 repeated here that seeds are, as a rule, either dicotyle- 

 donous or monocotyledonous. Some plants of the Pine 

 Family, however, have six cotyledons, whilst, on the 

 other hand, in the Orchids and a few other plants, these 

 organs are altogether wanting. 



253. The cotyledons vary greatly in thickness. In the 

 Maple, for example, they are very thin, while in the Pea, 

 the Bean, and the Oak they are extremely thick and 

 fleshy. 



254. Germination. If a seed is supplied with 

 proper warmth and moisture it soon begins to swell and 

 soften by absorption of water, with the effect of bursting 

 the seed-coats to a greater or less degree. At the same 

 time the process of growth is begun. This early growth 

 of the embryo is germination. The details of the process 

 vary somewhat according to the structure of the seed. In 

 dicotyledons, if the seed-leaves are thin and leaf -like, 

 containing within themselves but scanty store of nourish- 

 ment, the radicle will grow throughout its length so as to 

 raise the cotyledons above the soil, where they at once 



