CHAPTER III. 



NATURE OF FOOD STORED IN SEEDS AND OTHER 

 PLANT PARTS.* 



23. In the study of the parts of the seed it was found that 

 the seedlings are able to make considerable growth when not 

 supplied with food from the outside. This growth goes on at the 

 expense of food stored in the seed. This food was stored up in 



the seed during its formation in the ripening 

 of the fruit. In some seeds it is laid down 

 outside of the embryo and is called endo- 

 sperm, as in the grain of corn, wheat, 

 castor bean, etc. In others, while some of 

 it is formed as endosperm in the young 

 seed, it is largely or completely absorbed 

 by the embryo during the ripening of the 

 seed, as in the bean, pea, squash, sun- 

 flower, etc., where it is stored in the 

 cotyledons of the embryo. In the study 

 of the seeds we have found the general 

 location of the food substance. We wish 

 now to learn more particularly the form in 

 which it is stored, its nature, as well as the 

 special receptacles and their arrangement. 



The special receptacles are the ^cells of the endosperm, the 



cotyledons, etc., where the food is stored. 



24. Cells and tissues. A cell is a unit of microscopic struc- 

 ture in plants. It is like a minute box with cellulose for its walls. 



* It will probably be found convenient to study the nature and location 

 of food substances while the student is studying the various seeds, bulbs, 

 shoots, roots, etc., but this short chapter is introduced here in order to 

 avoid the unnecessary description of them with each different object studied. 



18 



ot 



Fig. 25. 



Section through grain of 

 corn. /. c. fruit coat; st. 

 starch, the aleurone layer 

 lies between the starch and 

 seed coats; cot. cotyledon 

 (here the scutellum); r. rad- 

 icle enclosed in root sheath; 

 pi. plumule. 



