46 THE TISSUES OP PLANTS 



the preparation of the nutritive material for the more per- 

 manent parts of the fabric, — ^this purpose being accomplished, 

 they die and are cast off from the organism to which they 

 are of no further use. Thus the starch cells of the cotyle- 

 dons perish as soon as the first pair of leaves, to whose 

 nourishment they contribute, are capable of absorbing the 

 nutritious gases of the atmosphere. So also the floral appa- 

 ratus fades after the germ is fecundated. Sometimes, how- 

 ever, after the corolla, stamens, and the upper part of the 

 pistil have perished, the vitality of the calyx remains unim- 

 paired; and seems to cooperate, with the green walls of the 

 pericarp, in the elaboration of those juices which are neces- 

 sary to the growth and maturation of the seeds contained 

 within its cavity. In the Witch Hazel, Hamamelis Vir- 

 ginica, the vitality of the leaves is exhausted in the deve- 

 lopment of the flowers, which do not appear until the former 

 decay and drop from the branches. The massive stem of 

 the tree is fabricated by the labors of the successive genera- 

 tions of leaves with which it was annually adorned. The 

 same law is manifested in the exuviation of the epidermal 

 appendages of the body of the inferior animals, such as hair, 

 feathers, teeth, horns, scales. These organs are thrown off 

 from the body in the fallj and their growth renewed in the 

 spring. The cells which form them have evidently a life 

 peculiar to themselves; their own period of growth, maturity, 

 decay, and dissolution, which is totally different from that of 

 the general Ufe of the organism with which they are con- 

 nected. • 



Thus not only the entire plant and animal, but its organs 

 separately and individually considered, are subject to certain 

 definite laws of development. The cells of animals and 

 plants do not therefore lose their individuality by being 

 associated. They have a life of their own, aa is manifest 



