638 CHEMICAL PROCESSES IN THE PLANT, 



and furnish the material for the formation of the protoplasm in the young cells of 

 the growing flower-stalk ; a large part is evidently employed in producing the grains 

 of chlorophyll in the foliage-leaves as they become green. Its function is now to pro- 

 duce at least as much formative material by assimilation as is required to build up the 

 transitory flower-stalk, and to supply it to the bulb. 



The ripe seed of Rkinus communis contains a very small embryo in the middle of 

 a very large endosperm ; neither contains starch, sugar, nor any other carbo-hydrate, 

 if we exclude the very small amount in weight of the cellulose of the thin cell-walls. 

 The reserve food-material consists of a great quantity of oil (as much as 60 per cent.) 

 and albuminoids, the admixture and composition of which have already been described 

 on p. 52. The very small quantity of these substances contained in the embryo would 

 only suffice for the first and very inconsiderable development of the seedling; its 

 enormous increase in size during germination must therefore be attributed almost 

 entirely to the substances deposited in the endosperm. The endosperm of Ricinus 

 enlarges very considerably, as Mohl first showed, during germination, and the material 

 required for its growth must therefore be diverted from the embryo. The tw^o thin 

 broad cotyledons remain in the endosperm, with their surfaces in contact with one 

 another, long after the root and the hypocotyledonary part of the stem have emerged 

 from the seed ; they are in contact by their backs with the tissue of the endosperm 

 which surrounds them on all sides, and absorb the reserve-materials from it, while 

 they keep pace slowly with its enlargement. When the parts of the seedling have 

 increased very considerably and the root has developed a number of lateral roots, 

 the hypocotyledonary portion of the stem elongates so that the cotyledons are drawn 

 out of the endosperm which is then completely emptied and reduced to a thin mem- 

 branous sac. They now rise above the ground, become expanded to the light where 

 they continue to grow rapidly and become green, to serve from this period as the 

 first assimilating organs. 



In this case, as in the germination of all oily seeds, sugar and starch are produced 

 here in the parenchyma of every growing part, disappearing from them only when the 

 growth of the masses of tissue concerned has been completed. Since the endosperm 

 grows also independently, starch and sugar are, in accordance with the general rule, 

 temporarily produced in it. The cotyledons apparently absorb the oil as such out of 

 the endosperm, whence it is distributed into the parenchyma of the hypocotyledonary 

 portion of the stem and of the root, serving in the growing tissues as material for the 

 formation of starch and sugar, which on their part are only precursors in the pro- 

 duction of cellulose. But in these processes of growth tannin is also formed which is 

 of no further use, but remains in the separate cells, where it collects apparently un- 

 changed until germination is completed. It can scarcely be doubted that the material 

 for the formation of this tannin is also derived from the oil of the endosperm, although 

 perhaps only after a series of metamorphoses. The absorption of oxygen, which is 

 an essential accompaniment of every process of growth and especially of germination, 

 has in this case, as in that of all oily seeds, an additional significance, inasmuch as 

 the formation of carbo-hydrates at the expense of the oil involves the appropriation 

 of oxygen. 



Since the metamorphoses of material proceed pari passu with the grow'th of the 

 separate parts, the distribution of the products of metastasis through the tissues is 

 continually changing, and can only be understood by a consideration of all the sur- 

 rounding circumstances. The micro-chemical investigation of seedlings in the state 

 represented in Fig, 442 //, gives, for instance, the following result : — in the endo- 

 sperm is found a great deal of oil and a little starch, with sugar at the outside; the 

 epidermis and parenchyma of the slowly growing cotyledons are filled with drops of 

 oil ; a large number of the epidermal cells contain tannin ; starch-granules are found 

 only in the parenchyma of the leaf-veins; the parenchyma of the hypocotyledonary 

 portion of the stem, which is at present growing the most rapidly, contains only 



