120 NATURE OF CASTOR BEAN SEED 



parallel to the leaves we see that the embryo consists of 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 

 forms the bulk of the seed, since it has been only partially con- 

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

 hard coat would prevent the access of water and gases. Observe, 

 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 be observed among seeds serv- 

 ing to convey water to the growing parts. Note the mucilag- 

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

 spongy rinds of the fruits of the walnut, cocoanut, etc. It is 

 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 be 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 

 parts permits their entrance. The breaking of the integument 

 would appear as a serious obstacle to the growth of the 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. The early growth of the embryo of the castor 

 bean is similar to that of the bean. The elongation of the lower 

 end of the hypocotyl pushes the root into the soil, while the 

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

 works the cotyledons and endosperm through the soil 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 is absorbed and but a papery skin remains 

 (Fig. 85, D). 



A grain of corn will illustrate another modification of the 

 seed. In this case the pistil remains in such close contact with 

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



