SEEDLINGS OF THE GRASS TYPE 



105 



in connection with it, there is a principle which is reckoned 

 with in growing certain plants of the Grass type. According 

 to the depth of planting this temporary stem region is long or 

 short. (Fig. 97.) This is due to the fact that the first node and, 

 consequently, the first of the permanent roots are always estab- 

 lished about the same distance under the surface of the soil, re- 

 gardless of the depth at which the seed was planted. Therefore, 



Fig. 99. — Stages in the development of the Onion seecUing. A, section 

 through an Onion seed showing endosperm {en) and embryo {c) with the 

 hypocotyl {h) and cotyledon (c) indicated. B, seed germinating; g, ground 

 Une; s, seed; c, cotyledon; h, hypocotyl; r, radicle. C, seedling more de- 

 veloped; c, cotyledon which is being pulled out of the seed; h, hypocotyl; 

 r, radicle; /, first leaf. D, a later stage of the seedling with cotyledon free 

 from the seed and permanent root system (p) developing. 



a deep permanent root system, which is often desirable in order 

 that the plant may withstand drought, is not secured by deep 

 planting — a fact which has been well demonstrated in case of 

 Corn and the small grains. Moreover, if the seed is planted too 

 deeply, its food and energy may be exhausted ])efore the plumule 

 reaches the light, in which case the seedling is unal>le to continue 

 its development. 



However, after the permanent roots are established they may 



