76 PLANT LIFE ON THE FARM. 



best grains from the largest and best ears, and repeated the 

 process year after year, just as the gardener has done for 

 countless generations in the case of fruits and seeds, as 

 the cattle-breeder does with Shorthorns or other pedigree 

 animals. These processes the farmer might with great ad- 

 vantage practise to a much greater extent than he usually 

 does, and thus secure hardy productive varieties best suited 

 to his particular conditions and best likely to fulfil his 

 requirements. 



Formation of the Embryo. The two processes of growth 

 and development may also be illustrated by recalling what 

 takes place in the germination of a seed. A ripe seed contains 

 within its coat or husk an embryo plant. Very often that 

 embryo plant is invested, as in the case of the grain of wheat, 

 with a whitish floury substance, known as the " perisperm." 

 All grass seeds have this perisperm surrounding their embryo. 

 A similar substance is found in the seeds of mangel ; the 

 seeds of turnips, peas, beans, and clover, on the other hand, 

 are destitute of it. An embryo plant consists of a radicle, 

 or rudimentary root, surmounted by a caulicle, which is 

 often so short as to be imperceptible to the naked eye, but 

 from which spring the seed-leaves, or cotyledons one only 

 in the case of all the cereals and grasses, two in the case 

 of the other crops of the farm. In the case of the wheat 

 grain, where the perisperm is abundant, the cotyledon is 

 small and thin ; but in the pea or bean, where the perisperm 

 is absent, the cotyledons are very thick and fleshy. The 

 difference depends upon the presence, in the one case, of 

 large quantities of reserve-materials in the embryo itself, 

 while in the case of the wheat the reserve-materials are 

 stored up in the perisperm. 



