GENERAL CHARACTERS OF THE ORDER 481 



The Fruit and Seed. — The fruit of grasses is in most cases 

 a caryopsis or a one-seeded form of nut, the seed of which has 

 grown completely into union with its surrounding thin pericarp. 

 The wheat grain discussed on p. 22 may be taken as typical of 

 a caryopsis and its enclosed seed. 



In young flowers the ovaries of the grasses are quite free from 

 the glumes and may remain so even when the fruit is ripe as in 

 the case of wheat, rye and oats; sometimes, however, during 

 growth after fertilisation the caryopsis grows up to between the 

 glumes and becomes united with the latter as in the case of 

 ordinary barley. 



In oats and many grasses the glumes so closely invest the 

 caryopsis that the latter does not fall out from the glumes when 

 the ripe panicles are shaken or thrashed ; nevertheless, in these 

 cases the caryopsis is free and easily separable from the glumes, 

 which is not the case in barley and many other grasses. 



The seed contains a large proportion of starchy endosperm, 

 at the side of which the embryo is placed. In some grass seeds, 

 and particularly those of certain varieties of cereal grains, such as 

 Hard wheats, the endosperm is flinty, or hard and semi-trans- 

 parent, while in others the endosperm, which is described as 

 mealy, is opaque and chalky when cut across. 



The different appearance of flinty and mealy endosperm is 

 due to the fact that in the first the starch grains within the" cells 

 are embedded in a dense matrix of proteid material, while in 

 the mealy endosperm the cells are not completely filled with 

 reserve materials, but very minute air spaces exist between the 

 starch-grains within the cells. 



The embryo (Figs. 7 and 151) possesses one cotyledon (the 

 scutellum), a short plumule, and in most cases a single primary 

 root covered by the coleorhiza. In the cereals and some other 

 grasses secondary roots appear upon the very short hypocotyl of 

 the embryo while the latter is still within the caryopsis and they 

 make their exit at the same time as the primary root, when 



2 H 



