22 



Introduction to Botany. 



this process of respiration which consumes oxygen and gives 

 off carbon dioxide (see Experiment 37), and in so doing 



makes active the internal energy 

 ^\ necessary to life and growth. 



In seeds having the reserve 

 materials stored in the cotyledons, 

 as in the Lima bean, the reserve 

 materials need only to pass from 

 these into the other parts of the 

 embryo, leaving the cotyledons in 

 a shrunken condition ; but in the 

 case of such seeds as those of 

 FIG. 4 . corn (Fig. 4) and castor bean, 



Median longitudinal section where the reserve materials lie 



through a grain of Indian corn. , . j r , , , r 



The median diagonal line de- outside of the embryo for the 

 marks the endosperm or reserve greater part, at least, the cotyle- 



food of the upper half from the , 11- 



embryo occupying the lower dons act as absorbing organs, 



half of the grain. The fleshy an d enlarge as germination pro- 

 cotyledon constituting the larger , , . , 

 part of the embryo surrounds CCeds SO as to keep in close COn- 



the plumule and hypocotyi tact with the diminishing food 



above and below. Photomi- ** 



crograph x 3. supply. This is also well illus- 



trated in the seed of the date, 



where the cotyledon is like that of the corn in serving 

 chiefly as an absorbing organ. 



In the seeds of the corn and date type the ferments lie 

 partly within the cotyledon and partly within the cells which 

 bear the food materials. As the reserve materials of the 

 date seed, consisting chiefly of cellulose of bony hardness, 

 become converted into sugar, they are absorbed by the coty- 

 ledon, which then enlarges and occupies the space thus 

 vacated (see Fig. 5). In this way the cotyledon keeps in 

 close contact with the reserve materials and transports 

 them from the seed as fast as they are rendered soluble ; 



