434 



BOTANICAL GAZETTE [may 



D 'Hubert (6) has made a study of fleshy plants with regard to 

 the formation of starch in the embryo sac. He finds that starch is 

 always present in the sacs of fleshy plants such as the Cactaceae, 

 Mesembrianthaceae, Crassulaceae, Portulacaceae, etc. He has 

 also found, however, that some non-fleshy plants show starch in the 

 embryo sac. According to D 'Hubert this latter case seems to be 

 the exception rather than the rule, and he beheves that there is 

 a relationship between the fleshiness of the plant and starch in the 

 embryo sac due to the slowness of the phenomena before fertiliza- 

 tion. This, however, receives very Uttle attention from him; 

 nevertheless it seems the more plausible theory. P. secundiflorus 

 is not a fleshy plant, but, judging from the drawings which 

 D 'Hubert has made of several fleshy plants, it has more starch 

 in its embryo sac than any of those figured. It appears that while 

 there is activity in the embryo sac very little if any starch is stored 

 up. As soon as the embryo sac matures and becomes inactive just 

 before fertilization, possibly due to delay in poUination, the stream 

 of nourishment which has been coming in cannot be checked 

 suddenly but keeps passing more and more nutrition into the inac- 

 tive sac, where it is stored in the form of starch. Such a conclusion 

 seems to be substantiated by the fact that activity in the sac brought 

 about by fertiUzation soon reduces the amount of stored-up starch. 

 Balicka-Iwanowska (2) has also investigated the deposition of 

 starch in "the embryo sacs of several plants, and has concluded 

 that starch is only found in the embryo sac when the tapetum is 

 cutinized. This does not seem to be the case in P. secundiflorus, 

 however, as the tapetum is undoubtedly not cutinized. Moreover, 

 it covers only half of the embryo sac, as has been explained before. 

 ScHMiD (12) has found starch present in the integuments as well 

 as the embryo sacs of a number of the Scrophulariaceae. He states 

 that the starch is found throughout the embryo sac, but that sooner 

 or later it is all translocated to the micropylar end, "wo die 

 lebhaftesten Teilungen stattfinden." 



The function of the tapetum seems to be one of nutrition, as has 

 been suggested by Balicka-Iwanowska (2). That it may have a 

 protective function, as has been suggested by Hegelmaier (7), 

 seems rather doubtful. This seems all the more questionable 



