122 COLLEGE BOTANY 



the groove. Tke single cotyledon or scutellum functions pri- 

 marily, if not entirely, as an organ for the absorption of the food 

 supply (Fig. 87). It never emerges and therefore never func- 

 tions as a foliage leaf. 



The Three Seed Types Compared 

 Bean Castor Bean Corn 



A true seed. A true seed. A fruit. 



Dicotyledonous. Dicotyledonous. Monoootyledonousv 



Food stores in cotyle- Food stored as an endo- Food stored as endo- 

 dons. sperm. sperm and in the nu- 



cellus. 

 Cotyledons serving for Cotyledons serving as Cotyledon serving as an 

 storage and as first absorbing organs and organ for the absorp- 

 leaves and then falling. as first leaves for a tion of the stored 

 long time. . foods. 



Environmental Factors in Seed Germination. — The ger- 

 mination of the seed is the growth of the embryo. In most plants 

 this is preceded by a period of rest. It is dependent on moisture, 

 warmth and oxygen, all of which are absolutely necessfl,ry. 



The moisture requirements which are necessary for germina- 

 tion vary greatly for the different kinds of plants ; some, such as 

 com and wheat, absorbing less than half their weight, others, 

 such as clovers, absorbing more than double their weight. The 

 water penetrates practiCT,lly the entire seed and softens prac- 

 tically all parts. 



^ Most seeds become swollen by the absorption of water and 

 certain germinating processes are started. The processes ai'e 

 mostly physical aad chemical and involve digestion and absorp- 

 tion of food, and gi'owth, waste and repair. They will receive 

 further discussion in Chapters XVIII and XIX. 



The temperature necessary for germination is also extremely 

 variable for the seeds of various kinds of plants, the optimum 



