380 BOTANICAL GAZETTE [November 



megaspore produces the 8-nucleate sac there are three such divi- 

 sions; when a similar sac arises from a daughter cell, two mega- 

 spores thus taking part in the process, there are two divisions; and 

 when the megaspore mother cell gives rise to the sac directly, four 

 megaspores are involved and the egg is separated from the mega- 

 spore by but one division. 



The tendency to mature the egg earlier and earlier in the 

 ontogeny of the gametophyte is very conspicuous among gymno- 

 sperms, and it was hoped that among these very advanced angio- 

 sperms the end result of this specialization might be found— the 

 megaspore itself functioning as an egg. The number of cases in 

 which the elimination of but one more division would result in this 

 situation is fairly large, and includes sacs with 4 nuclei {Cyprt- 

 pedium, Pace 7), 8 nuclei (Lilium, various orchids, and many 

 others), and 14 nuclei (Pandanus, Campbell 3). That the reduced 

 condition is being approached by such a variety of ways allows us 

 to expect with confidence to discover in some plant a situation 

 exactly paralleling that in animals, in which the product of the 

 reduction divisions at once becomes the egg. 



Scarcely less striking than the variability within the species is 

 the uniformity shown by the embryo sac throughout a group so 

 varied in structure and habit as the orchids. In spite of the incon- 

 stancy in the methods of sac development the end result is remark- 

 ably uniform. The ordinary 8-nucleate sac, developed from a single 

 megaspore, is the prevailing condition in the group. Beside the 

 species here reported, it is found in Calopogon (Pace 8) , Habenana 

 (Brown i), Epipactis (Brown and Sharp 2), Gymnadenia (Ward 

 10), Orchis (Strasburger 9), and others. 



The influence of the surrounding conditions upon the behavior 

 of the nuclei during the formation of the embryo sac has recently 

 been considered in some detail (Brown and Sharp 2). The facts 

 brought out in the present account lend further support to the idea 

 there expressed, namely, that the causes for the behavior of the 

 nuclei are to be sought largely in factors external to the nuclei 

 themselves. The conditions under which the ovules of orchids 

 develop within the ovary are undoubtedly much the same in the 



