Study of Reproduction in the Genus Acer 129 



function, also deserves consideration. Such material as the 

 writer has favors the interpretation here offered, but it is not 

 sufficiently conclusive to serve as a basis for discarding the state- 

 ment of Mottier, and thequestion must be left open for the present. 



In any event, by the time the row of three cells is formed, 

 the ovule begins to bend downward, and the outer integument 

 on the lower side of the ovule begins to enlarge decidedly (Fig. 

 88). Bv the time the chalazal cell of the row of three has under- 

 gone the first division the ovule has increased greatly in size, 

 bent over nearly as far as it ever does, and it is evident that the 

 degeneration of the two cells at the micropylar end of the row 

 of three is far advanced. From the swelling of the outer integu- 

 ment the cells grow as hair-like processes (Fig. 89). The divi- 

 sion into the four nucleate stage shows these hair cells even more 

 elongate, and beginning to become crowded at the bottom of 

 the ovarian cavity (Fig. 90). They subsequently form a mass 

 of considerable size, and about the time of fertilization their 

 walls seem to be thickened in a gelatinous manner, and evidences 

 are present that the cavity of the ovary contains a partlv coag- 

 ulable liquid. The hairs may secrete a fluid which aids in the 

 passage of the pollen tube to the micropyle. 



There is rarely any evidence of the degenerating cells bv the 

 time the eight nucleate stage of the embryosac has been reached. 

 Of these eight nuclei, three pass to the antipodal end and or- 

 ganize cells the membrane of which often is very indefinite. 

 Two form synergida? and one an egg at the micropylar end, 

 the latter protruding into the embryosac cavity above the 

 synergidse. Two nuclei remain, one at each end of the sac 

 (Fig. 36). These polar nuclei pass toward the center of the 

 cavity, where they come into contact (Fig. 37), and then pass 

 together to the egg, usually not fusing till they have taken up 

 a position close above it (Figs. 38, 39). Fusion is by simple 

 merging of the contents, no definite spireme being in evidence 

 at this time (8). This stage is generally not reached till after 

 the flowers have opened, and even till after pollination has taken 

 place. The antipodal cells very soon disappear, though thev 

 mav in occasional cases persist for some time (3). 



Fertilization and Embryogeny 

 The fusion of the gametes in Acer, so far as observed, re- 

 sembles the conditions described bv Ishikawa for Oenothera (8). 

 The pollen tube in entering destroys usually only one of the 



