ASSIMILATION AND METASTASIS. 



715 



which serve to protect the new bulb ; the inflorescence subsequently dies down. The 

 reserve-materials which accumulate in the daughter-bulbs are partly derived from those 

 of the mother-bulb ; but are completed by the products of assimilation of the green 

 leaves of the flower-stalk. When the flower-stalk has also died down, nothing remains 

 of the whole plant but the bud which has developed into a new bulb. For a time it 

 does not put out any new organs, but is apparently dormant ; but in the interior the 

 end of the stem continues to grow slowly, and produces new rudiments of leaves and the 

 flower-bud for the next year ; when the process now described is repeated. 



So far we have only pointed out the rela- 

 tion of the starch and of the sugar produced 

 from it to the growth of the plant ; there are 

 formed however along with it, and probably 

 likewise at the expense of these carbo-hydrates, 

 other substances, such as the colouring matter 

 of flowers, the oil in the pollen-grains, &c. 

 The albuminoids at first contained in the bulb- 

 scales become transported to a distance from 

 them, and furnish the material for the forma- 

 tion of the protoplasm in the young cells of 

 the growing flower-stalk ; a large part is evi- 

 dently employed in producing the chlorophyll- 

 granules in the foliage-leaves as they become 

 green. Their function is now to produce at 

 least as much formative material by assimila- 

 tion as is required to build up the transitory 

 inflorescence and to supply the bulb. 



2. The ripe seed oi Ricinus communis con- 

 tains 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 quan- 

 tity of oil (as much as 60 per cent.) and albu- 

 minoids, the admixture and composition of 

 which have already been described on p. 53. 

 The very small quantity of these substances 

 contained in the embryo would only suffice 

 for the first and very inconsiderable develop- 

 ment of the seedling ; its enormous increase 

 in size during germination must therefore 

 be attributed almost entirely to the sub- 

 stances deposited in the endosperm. The 

 endosperm of Ricinus enlarges very consider- 

 ably, as Mohl first showed, during germina- 

 tion, and the material required for its growth 

 must therefore be diverted from the embryo, 

 in the endosperm, with their surfaces in 



Fig. 470. — Longitudinal section through a germinating 

 bulb of Tiilipa pracox : k the brown enveloping membrane, 

 k the flattened stem which forms the base of the bulb and 

 bears the bulb-scales sh; si the elongated part of the stem 

 which bears the foliage-leaves /' /', and terminates in the 

 flower ; c the ovary, / perianth, a anthers ; 2 a lateral bulb 

 in the axil of the youngest bud-scale, which developes into 

 tlie bud of next year's bulb ; w the roots which spring from 

 the fibro-vascular bundles of the base of the bulb. 



The two thin broad cotyledons remain 

 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 hypocoty- 

 ledonary portion of the stem elongates so that the cotyledons are drawn out of the 



