140 STRUCTURAL BOTANY 



becomes free curves, so that its tip is directed straight 

 downwards, and at once penetrates the soil (see Fig. 

 51). As soon as this has happened, the young root 

 immediately begins to develop root-hairs, which take 

 a firm hold of the particles of soil, and serve both for 

 nutrition and for the fixing of the plant during its 

 subsequent growth. Meantime the hypocotyl grows 

 very rapidly, and curves so that the apex of the stem 

 comes to point directly upwards. The cotyledons for 

 a time remain imprisoned in the seed-coats, which are 

 lifted up with them, above the level of the ground, but 

 they soon spread themselves out flat, and in doing so 

 strip off the seed-coats. 



We see, then, that in germination the root grows 

 vertically downwards and the stem vertically upwards, 

 while the cotyledons take an approximately horizontal 

 position. The apex of the stem (the plumule) now 

 begins to develop further and forms leaves. The 

 root at the same time begins to put out lateral 

 branches, and we may now regard germination as 

 completed; the embryo has become a seedling (see 

 Fig. 30, p. 79). 



The food - supply necessary for germination is 

 obtained at first from, the organic substances (starch, 

 etc.) stored up in the cotyledons themselves, and in 

 part also from the remaining layer of endosperm, 

 which, as we saw above, is rich in proteid granules. 

 As soon as the root-hairs have taken hold of the soil, 

 the seedling can begin to supply itself with mineral 

 food, but it is only when the cotyledons have ex- 

 panded and become green that carbon-assimilation can 



