106 



GERMINATION OF SEEDS: SEEDLINGS 



be put deeper in the soil by adding dirt around the plant. In 

 semi-arid regions where a deep permanent root system is desired, 

 the ground is often listed, that is, plowed into deep furrows, and 

 the Corn planted in the bottom of the furrows. Then as the 



furrows are gradually 

 filled in cultivation, the 

 permanent roots are 

 buried deeper in the 

 soil, where there is a 

 chance for moisture 

 during drought. In this 

 same connection, one 

 can see some advan- 

 tage in drilling small 

 grains in that the roots 

 of the plants will be 

 buried deeper as the 

 dirt from the ridges is 

 carried into the drill 

 furrows during rains 

 and thaws. 



In the small grains, 

 such as Wheat, Oats, 

 Barley, etc., although 

 the temporary system 

 is just as prominent as 

 in Corn, there is, how- 

 ever, a difference of 

 minor importance to be 

 noted in the number 

 of primary roots, which 

 is one in Corn but two 

 or more in the small 

 grains. {Fig. 98.) 



Fig. 100. — Stages in the development of a 

 Common Bean seedling. A, the cotyledons 

 (c) being pulled out of the ground by the hy- 

 pocotyl (h). t, testa; r, radicle; a, root hairs; 

 g, ground Une. B, the hypocotyl has straight- 

 ened, and the cotyledons have shed the testa 

 and spread apart, thus giving freedom to the 

 plumule (p). C, stage with plumule develop- 

 ing stem and leaves (J), root system much en- 

 larged by secondary roots (s), and cotyledons 

 (c) shrinking through loss of stored food. 



The presence of the 

 temporary system, although occurring in other plants, is a not- 

 able feature of the Grass seedlings. Another feature to be noted 

 is that the cotyledon remains where the seed was placed in 

 planting, that is, it is not pushed up out of the soil by an elong- 

 ating hypocotyl. 



