The Plantlet. 



.'57 



the bean and pumpkin, are planted in soil, the cotyle- 

 dons must be forced through the soil above them, an 

 act requiring considerable en- 

 ergy. If such seeds are covered 

 with much soil, the plantlet is 

 often unable to lift its cotyle- 

 dons to the surface, and hence 

 must perish. Fig. 12 shows two 

 bean plantlets that tore off their 

 cotyledons in the vain attempt 

 to lift them through five inches 

 of soil. The plantlet of wheat, 

 barley and oats, though much 

 smaller and weaker than that of 

 the bean, readily grows through 



Fl Jl2. Showing two bean this de P th f Soil > beC&USe the 

 plantlets that tore off their finv -nmntpr^ shoot (nlnrnnlp 

 cotyledons from being too CmV P 01 



(55) ) of these plants readily in- 

 sinuates itself between the soil particles and comes to 

 the surface with little expenditure of energy, even when 

 deeply planted. Plantlets of the larger beans usually 

 fail if the seeds are planted three inches deep in a 

 clay soil that bakes above them. Those of the castor 

 bean,* though very robust, can hardly lift their cotyle- 

 dons through one inch of soil, while those of the pea, 

 though much more slender, readily grow through four 

 to six inches. Apple seeds planted in autumn on clay 

 soil, usually fail to germinate the following spring 

 unless covered with sand or humus, or carefully 

 mulched, because the plantlets are unable to lift their 

 cotyledons through a baked surface soil. 



* Ricinus. 



