DISPERSION AND GERMINATION OF SEEDS. 229 



dextrine and sugar have precisely the same chemical composition 

 as cellulose. Thus it is, that thfr store of nutritive, though 

 unassimilated and insoluble starch, with which the seed is so 

 copiously provided, is by the forces of nature rendered soluble, 

 and converted into dextrine, sugar, and finally cellulose, the 

 substance which constitutes the very basis of all the vegetable 

 tissues, it becomes the source from whence the embryo derives 

 the materials of its nutrition and increase. 



These chemical changes in the substance of the seed soon 

 awaken its dormant vitality. We see the radicle of the embryo 

 descend through its swollen and ruptured integuments into the 

 earth, whilst at the same time the plumule rises into the atmo- 

 sphere, carrying up with it the young cotyledons, which soon 

 unfold in the form of two white and opposite leaves above the 

 earth's surface. Exposed to the action of light we see them 

 gradually change their color, chlorophyl being deposited in 

 their superficial cells. The cotyledons appear to be only, 

 indifferently adapted to the aerial medium into which they are 

 elevated, and hence, as we have seen, they sometimes continue 

 below the ground without any detriment to the growth of the 

 young embryo. When, however, the gemmule or bud at the 

 summit of the plumule elongates and the true and permanent 

 leaves of the plants appear, they perform the functions of 

 aerial leaves in a much more perfect manner ; at the same 

 time, from the other extremity of the axophyte, additional 

 roots are developed, and the organs at both extremities are 

 beautifully adapted to their respective media. Grermination 

 is now completed, the cotyledons and other appendages of 

 the embryo decay and disappear, having performed their 

 respective functions, and the young plantule, rejoicing in all 



