510 



ON SEEDLINGS 



attained nearly their full size, but had not yet reached matu- 

 rity. Neither the placenta nor the original and true cavity 

 of the ovary are shown in this section, because they were 

 situated at a higher level. The ovule from the first was basal, 

 and the seed, even at maturity, may be looked upon as lying 

 astride the basal placenta, with its four lobes projecting into 

 as many cavities excavated from the originally solid base of 

 the fruit. The testa is shown at T, lining the interior of the 

 cavities and enclosing the variously folded lobes of the coty- 

 ledons (C, C,C,C). The walls surrounding the cavities are thick 

 and sclerenchymatous, with exception of the thin outer rind 



and its appendages, 

 the bracteoles or wings, 

 shown at B', B'. The 

 cotyledons of the em- 



^^ / ^^) 11 br y diver S e > one to 



each side of the fruit, 

 and their lobes pass 

 in pairs into each of 

 its four cavities. As 

 growth proceeds and 

 the short lobes become 

 too wide for the cavi- 

 ties, they become COn- 

 FiG. 6W.-Pterocarya caucasica. Transverse sec- d^Hr.a.tfl i n order to 



them- 

 selves to the restricted 

 space and at the same 



time to fill it. The secondary fission seems intended to 

 facilitate folding, and was probably originally brought about 

 by excessive plication. If the two lobes had been in one piece, 

 the latter would have had to be twice conduplicate longitudi- 

 nally, which would have been difficult to accomplish. The 

 folding is not always on the same plan, as may be seen by 

 reference to the figure. 



The Walnut (Juglans). The fruit of the Walnut differs 

 from that of Pterocarya in several remarkable particulars, and 

 while the cotyledons of Pterocarya are leaf-like and aerial in 

 germination, those of the Walnut never emerge from the seed. 



Transverse sec- 

 tion through a more advanced fruit near the base, 



x e. (Sept. 21.) T, testa ; c, c, c, c, folds of accommodate 



cotyledons ; B', B', bracteoles or wings ; Ca, small 



mass of cortical tissue. 



