i-o NATURE « >1 CAST< >R BEAN SEED 



parallel to the leaves we see that the embryo consists ol a very 

 small stem and two delicate leaves imbedded in an oily tissue, 

 the endosperm (Fig. 85, B), In the bean the seed consisted of 

 an embryo and integument. In the castor bean, the endosperm 

 lorms the hulk of the seed, smce it has been onlj partially con- 

 sumed by the embryo. It would naturally he inferred that the 

 hard coal \\<»uld prevent the access of water and ( foserve, 



however, that the caruncle readily absorbs water and that the 



embryo and endosperm are in direct contact with this region 

 of the seed. Many devices will he observed among seeds serv- 

 ing to convey water to the growing part-. Mote the mucilag- 

 inous coats on flax, quince, many mustard seeds, etc.. or the 

 spongy rinds of the fruits of the walnut, cocoanut, etc. It i- 

 well worth your time to submerge in water colored a deep red 

 with eosin widely different seeds and examine them from time 

 to time, noting the period required for the penetration of water 

 and the lines along which the water enters and is distributed. 

 It will he found that many seeds and fruits exclude water and 

 oxygen very effectively for one or more years with the result 

 that the renewal of growth is delayed until the decay of the 



part-> permit- their entrance. The breaking of the integument 

 would appear as a serious obstacle t-> the growth of tin- embryo. 



However, the power generated by the cells owing to their ex- 

 pansion through the absorption of water is quite sufficient to rup- 

 ture the seed coat. Tin- early growth of the embryo of the castor 

 bean is similar to that of the bean. Tin- elongation of the lower 



end of the hypOCOtyl pushes tin- root into the soil, while the 



upper end of the hypocotyl, arching and twisting as it elongates, 



works the cotyledons and endosperm through the -oil into the 



air (Fig. 85, C). In this seed the food is without the cotyle- 

 dons. Consequently, although the cotyledons gradually enlarge 

 and become green, they remain in contact with the endosperm 



until all its food i- absorbed and hut a paper} -kin remain- 



(Fig. 85, D). 

 A grain of corn will illustrate another modification of the 



Seed. In this case the pi-til remain- in -uch close contact with 

 the seed thai it appears to form an additional integument. Such 



