ELEMENTS OF STRrCTURAJ, IIOTANY. 07 



coats, either to such a degree as to Hberato the cotyle- 

 dons comiiletely, or so as to permit the escape of the 

 radicle acd the plumule. The former immediately 

 takes a downward direction, developing a root from its 

 lower end, and either elongates througii its whole 

 length, in which case the cotyledons are pushed above 

 the surface, as in the Beau, or remains stationary, in 

 which event the cotyledons remain altogether under 

 ground, as in the Pea and in Indian Corn. 



]iefore the root is developed, and the little plantlet 

 is tliereby enabled to imbibe food from tiie toil, it has to 

 depend for its growth upon a store of nourishment 

 supplied by the parent plant before the seed was cast 

 adrift. The relation of this nourishment to the embryo 

 is different in different seeds. In the Bean and the 

 Pumpkin, for example, it is contained in the cotyledons 

 of the embryo itself. But in Indian Corn, as we have 

 already seen, it constitutes the bulk of the seed, the 

 embryo merely occupying a hollow in one side of it. In 

 such cases as the latter, it will be remembered that the 

 term albumen is applied to the nourishing matter, as 

 distinguished from the embryo. 



159. As to the number of cotyledons, it may be re- 

 peated that, as a rule, seeds are eitlier dicotyledonous 

 or monocotyledonous. Some plants of tlie Pino Fam- 

 ily, however, exhibit a moditication of the dicotyledo- 

 nous structure, having severak cotyledons, and being 

 consequently distinguislied tks polyivtyU^donous. 



