THE FEMALE GAMETOPHYTE 



85 



in the latter the two outer begin the formation of embryo-sacs; 

 and in Eriobotrya Guignard 12 found that while ordinarily the 

 innermost megaspore of three functions, the middle or the outer 

 one may form the embryo-sac, and even all three may begin its 

 formation. The same author x l also reports great irregularity 

 in Acacia, in some species the innermost of four megaspores 

 functioning, in others the next outer one, and in still others 

 the middle one of a row of three. In 

 Loranthus also, Treub 13 finds that the 

 outermost megaspore of three persist- 

 ently functions. Among the Aralia- 

 ceae (Ducamp 112 ) usually the inner- 

 most of four megaspores functions, but 

 occasionally one of the middle cells 

 may become the embryo-sac. Such 

 cases serve to emphasize the megaspore 

 character of all the cells of the row\ 



Among the Sympetalae, the only 

 well-established exception is that of 

 Trapella, in which Oliver 21 finds that 

 the outermost of four megaspores func- 

 tions, and in one case the next cell, 

 while the innermost megaspore devel- 

 ops the remarkable haustorium (Fig. 

 32). In Asclepias tuberosa, although 

 the innermost of the row of four mega- 

 spores ordinarily functions, Frye 118 

 has observed cases in which the outer- 

 most megaspore functions, and others 

 in which the two innermost develop 

 together; while Yesque 4 reports that 

 in Salvia pratensis the outermost of 



the four megaspores functions. In Crucianella (Lloyd 105 ) 

 all four megaspores, which in this case are not separated by 

 cell-walls, may begin to germinate (Fig. 33). Guignard 12 

 also includes Pyr<Hlivum as among the forms whose outer- 

 most megaspore functions, but it needs further investigation. 

 It should be noted in this connection that when a row of four 

 megaspores is to be formed, the nucleus nearest the chalaza al- 

 most invariably shows a more advanced stage in mitosis than 



Fig. 32. — Trapella sinensit. 

 Ovule some time after fer- 

 tilization : m, micropyle ; s, 

 synergids ; .<•/<, suspensor ; g, 

 embryo ; e, endosperm ; v, 

 vascular bundle ; c, two long 

 cells resulting from the lon- 

 gitudinal division of the low- 

 ermost megaspore of a row 

 of four; x 100.— After Oli- 

 ver." 



