PART U.] 



INTRODUCTION. 



233 



sufficiently developed to absorb moisture. To 

 supply the wants of the young plant while it 

 remains in this feeble and imperfect state, a 

 quantity of albumen is laid up in the seed; and it 

 is evident that this substance must be extremely 

 nourishing, as it forms, when ground, what we 

 call flour. The young plant is thus provided 

 with food, till its roots are sufficiently developed 

 to obtain it from the soil ; and to enable it to 

 elaborate this food and to turn it into sap, it is, 

 in most cases furnished with one or more seed- 

 leaves, or cotyledons, 

 (see c in Jig. 102,) 

 which drop off as soon 

 as the true leaves are 

 sufficiently advanced 

 to be able to perform 

 their proper functions. 

 The cotyledons differ 

 in number, form, and 

 substance in the dif- 

 ferent genera ; but in 

 all plants, they are very 

 different from the true 

 leaves, being admirably contrived for answering 

 the end for which they are designed ; and 

 it having been found that the plants having 

 two or more cotyledons differ widely in many 

 other respects from those having only one coty- 



FlG. 102,— COTYLKDONS, LEAVES, 



AND Wood of a Dicotyledonous 

 Plant. 



