Vegetable Physiology. 367 



contained in the seed is sometimes absorded into the tissue of 

 the cotyledons, rendering them thick and fleshy, as in the Pea 

 and Bean. In this case the cotyledons, with the small germ 

 to which they belong, fonn the entire contents of the seed. In 

 other instances, however, they are thin leafy organs, and oc- 

 cupy, with the germ, but a small part of the seed. The re- 

 mainder then consists of a separate store, which is termed the 

 albumen. This is the case in all monocotyledonous seeds, and 

 in some dicotyledons, as the Ash and Horse-Chestnut. 



Between the cotyledons, (taking a bean as the subject of ex- 

 amination,) is the real germ ; the upper extremity of which, 

 called the plumula, subsequently developes itself into the stem, 

 and puts forth leaves ; whilst the lower part, or radicle, which 

 is always directed towards the foramen, becomes the root. 

 The plumula sometimes presents the appearance of the 

 plant in miniature ; its leaves and buds being quite discern- 

 ible, though on a very small scale. The subsequent devel- 

 opement of the germ into the perfect plant, is that which in 

 its early stage, is called germination. When a seed like that 

 of the bean begins to germinate, it first swells and bursts its 

 seed-coats; the plumula then extends upwards, bringing the 

 cotyledons just above the surface of the ground ; whilst the 

 radicle penetrates downwards. In some plants, however, the 

 cotyledons remain underground, as in the Oak ; and there are 

 a few in which they appear entirely absent. The cotyledons 

 when exposed to the light, become green ; and perform for a 

 time (though imperfectly) the functions. of leaves, at the same 

 time yielding to the young plant, the nourishment they con- 

 tain. By the time this is exhausted, the true leaves and roots 

 are sufficiently developed for the support of the structure ; and 

 the cotyledons, being then no longer required, decay away. 

 In the seeds of monocotyledons, the albumen is always sepa- 

 rate, and the embryo, which occupies but a small proportion 

 of the whole mass, cannot always be readily distinguished in 

 the midst of it, until germination commences. The cotyledon 

 at first completely sheaths the plumula, which afterwards 

 pierces it, and unrols its first leaf. 



The conditions requisite for the germination of the seed, are 



