646 PHYSIOLOGY. 



tion of starch into sugar, but also of fibrine into peptone. A. similar 

 formation of ferments has been observed in the case of leaf-buds about to 

 develop (Kossmann). As the seedlings grow and become exposed to the 

 light, the asparagin disappears. 



During germination Boussingault observes that the plant comports it- 

 self as an animal does, or like an egg during incubation. It grows on the 

 reserve materials accumulated in the tissues, oxidizes them, emits carbonic 

 dioxide, evolves heat, as happens in other chemical changes, the final re- 

 sult being the nutrition of the embryo plant. 



The Perisperm. With reference to the part played by the perisperm, it 

 may be stated that it is a store-house of nourishment upon which the 

 young seeds draw before they have acquired the power of feeding for 

 themselves. Hence we often find that in the case of those seedlings which 

 have from the first a well-developed feeding-apparatus in the shape of 

 green seed-leaves (as in the Turnip, Mustard) the perisperm is at the time 

 of germination either non-existent or in very small proportion. On the 

 other hand, where the perisperm is abundant, there the seed-leaves are 

 very small and inconspicuous. The difficulty in inducing some seeds to 

 germinate is connected with the fact that the seedling plant is often able 

 to feed upon the perisperm, but is not able to shift for itself ; hence when 

 the supply of albumen is exhausted, the seedling fails. M. Van Tieghem 

 has lately made some experiments with a view to ascertain how the seed- 

 ling plant gets its nourishment from the perisperm, and in the course of 

 his experiments ascertained that the perisperm in some cases acts as a 

 nursing mother to the young embryo, while in others the young plant 

 merely helps itself to what it finds at hand. Albumen of an oily character 

 undergoes a change of structure and composition digests itself, in fact; 

 and the young plant does but take up the products of this change in the 

 tissue and constitution of the perisperm. 



Floury perisperm, such as that of the Wheat, is passive. It is changed 

 and ultimately absorbed and digested by the embryo itself. It is of the 

 nature of food simply, and does not, as in the former case, also fulfil the 

 office of a nursing mother. The germination of seeds and the length of 

 time required for the process are thus seen to depend very materially on 

 the nature of the perisperm. 



Independence of the Parts of the Embryo. M. Van Tieghem has ascer- 

 tained that, under certain circumstances, the several parts of the embryo 

 plant may be severed one from the other, and even themselves divided 

 into fragments, and yet these fragments will preserve their vitality and 

 grow independently. The cotyledons, if divided, will produce radicle 

 and buds ; thus a plant of a Sunflower was made to produce eight plants 

 by dividing each of its two cotyledons into four. When the perisperm was 

 removed from around the embryo of a Marvel of Peru, germination went 

 on well for a time, but the plumule was arrested in its development, so 

 that the perisperm seems to be required for the formation of the plumule, 

 though the other parts of the embryo obtain sufficient nutriment from the 

 stores accumulated in their own tissues. The same experimenter ex- 

 tracted embryos from the seeds, and placed them in an artificially pre- 

 pared substance, resembling in constitution the perisperm, and he found 

 that the embryos absorbed the artificial food and used it up in the pro- 

 duction of new tissues, j ust as they would have utilized the stores in the 

 perisperm. 



