128 MISSOURI BOTANICAL GARDEN, 



Finally the tissue beneath it is undermined, and so a single 

 antipodal cul-de-sac is formed, which continues its growth 

 upward and toward the raphe. During this time the tissue 

 about the cul-de-sac shows a reducing action on Fehllng's 

 solution. The cell walls are swollen, and stain deeply with 

 Bismarck brown. Thus we may infer that active digestive 

 processes are in progress; but we are not, of course, able to 

 say whether the reaction is one to tannin alone, or to a reduc- 

 ing sugar, or both. The cul-de-sac is therefore a haustorium, 

 for a prolonged period constantly encroaching upon the sur- 

 rounding tissues. Its size increases as the seed enlarges till 

 its dimensions are sufficient to make it a prominent feature 

 of the mature seed (figs. 5, 6, 7, 10, 13, 12). It is impor- 

 tant to notice in this connection that, resulting from the 

 stimulus of the growing cul-de-sac, the surrounding chalazal 

 tissue increasing concomitantly by cell division, its cells 

 become radially disposed. These always contain tannin, 

 the least densely filled cells being those next to the endosperm. 

 A part, at any rate, of the food material supplied to the 

 endosperm is a tannoid substance and this passes over into 

 the endosperm chiefly at the cul-de-sac. As we shall see, a 

 tannin is also present in the endosperm during some part 

 of its development. That the chalazal cul-de-sac is the active 

 center for the distribution of nutrients is indicated also by 

 the circumstance that it is the center from which progress 

 the physiological as well as anatomical changes which over- 

 take the developing endosperm; and by the further fact that 

 the remaining tissues contingent on the embryo-sac grow, 

 pari passu, with the endosperm. 



Why the endosperm digests the tissue touching it at one 

 point and not at another is an interesting and important 

 question, which has received little attention. The same 

 question applies to the embryo-sac, during its development 

 in many instances ; and similarly to the developing embryo. 

 I have elsewhere 20 shown that the embryo-sac may develop 

 in a quite abnormal manner in this regard and behave much 

 as a pollen tube, but in a more aimless fashion, so to speak. 



20 Lloyd, 1902. 



