18 Botanical Section [pti 



The naked grain of grasses forms a special type of fruit techni- 

 cally known as a caryopsis. It is a one-seeded, dry, indehiscent 1 

 fruit, with the fruit- wall (pericarp) fused to the seed-coat (testa). 

 The true seed then, consists of the embryo with its store of 

 endosperm, enclosed within the seed-coat. The thin fruit-wall 

 surrounding the seed-coat makes up the complete grain. The 

 embryo forms but a small portion of the entire grain, the bulk of 

 the latter being composed of the starchy endosperm, reserved 

 for the nourishment of the seedling during the early stages of 

 its growth. If the embryo is examined under the microscope 

 it is seen to consist of a primary shoot (plumule), a primary 

 root (radicle) — often with secondary rootlets visible — and of a 

 flat shield-like structure, one face of which is applied to the mass 

 of endosperm. This organ is known as the scutellum, and is 

 generally regarded as the cotyledon. 



Figs. 20 and 21 give longitudinal and transverse sectional 

 views of cereal grains, and show the position and parts of the 

 embryo, and also the different parts or layers of the rest of the 

 grain. 



CHAPTER II 



GENERAL BIOLOGY OF GRASSES 



In this chapter it is only intended to deal briefly and in a 

 general way with the development and functions of the different 

 organs. For fuller details of the physiology of grasses reference 

 must be made to special works on that subject (see also Biblio- 

 graphy, Nos. 10, 34). 



Germination. The "seeds" of grasses — like those of other 

 plants— require as essentia] for their germination (1) moisture, 

 (2) a suitable temperature, (3) the presence of air or oxvgen. 

 Other factors may influence the rapidity of the process, or the 

 percentage of germination, but these three are essential to it. 

 The most favourable temperature for the germination of most 

 grass "seeds" lies between 20° and 25° C. Under such conditions 



1 A few exceptions occur in exotic species. 



