vi.] BOTANY. 27 



the plant; the scales are undeveloped leaves. To 

 ascertain which is the radicle and which the plumule 

 of the plantlet, the seed must sometimes be examined 

 soon after it has germinated, when they are easily 

 distinguished, whether by their form or by the direc- 

 tions they take. 



37. This elongation of plumule and radicle is the 

 first growth made by both the pea and the mustard 

 but after this they follow quite different modes of 

 development. 



In the case of the pea the cotyledons do not grow 

 at all, but supply nourishment to the growing radicle 

 and plumule, which absorb it through the points of 

 union ; after which, their nourishing matter being ex- 

 hausted, the cotyledons shrivel and dry up, or rot. 

 The plantlet thus feeds on the same substance as is 

 eaten at table, and in so doing it empties the cells of the 

 cotyledons of the starch, oils, albuminoids (Sect. 17 to 

 20) which they contained. Here, then, the cotyledons 

 nourish the plumule and radicle from the very first. 



In the case of the mustard, on the other hand, 

 whilst the radicle plunges into the soil, the coty- 

 ledons are carried up above ground, where they 

 spread out to the light, become green, and assimilate 

 for the plantlet, as leaves do for full-grown plants. 



38. In the wheat (Fig. 12), the plantlet lies on one 

 side of the seed, between its integument and the albu- 

 men, which is white and floury. It has not two oppo- 

 site thick cotyledons, but one, which forms a sheath 

 around the other leaves of the plumule. When germi- 

 nation begins, the plumule and radicle absorb nourish- 

 ment from the albumen by contact, and not through a 

 connecting structure such as that which unites the 



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