388 THE SEED AND ITS GERMINATION 



C. THE CASTOR-OIL PLANT (Ricinus) : A seed with oily endosperm 

 and epigeal cotyledons. 



(5) Remove the mottled brittle testa (with its wart-like swelling 

 at one end) from the seed, exposing the white mass of oily endo- 

 sperm : split this open very carefully and observe the embryo 

 in the middle. The very thin membranous cotyledons are 

 extremely delicate and easily tear. They extend almost the 

 whole length of the seed and have a complete system of veins 

 already developed. Draw the embryo, noting the short cylindrical 

 hypocotyl, continuous with the radicle, and the epicotyledonary 

 bud. 



(6) Sketch a series of stages in the development of the seedling, 

 showing the gradual straightening and elongation of the hypocotyl 

 (which may reach a length of 8 to 12 inches and a considerable thick- 

 ness), the large flat cotyledons and the development of the epicotyl- 

 edonary shoot. Note the buds in the axils of the cotyledons and 

 the well-developed root system. 



(7) If available, compare maize, wheat and date seedlings, 

 showing endosperm and "sucking" organs : also the very small 

 seedlings with epigeal cotyledons of some of our common weeds 

 and garden crops. 



