Study of Reproduction in the Genus Acer 131 



dition appears long before the length of the embryo equals that 

 of the cavity, in Acer rubrum. The form of the embryo differs 

 somewhat among the various species even in the early stages 

 (Figs. 49, 50). 



In most species the ovary did not grow much faster than 

 necessary to accommodate the swelling ovules, but in others, 

 Acer negundo especially, immediately after fertilization the 

 ovarian cavitv increased at a much greater rate than the ovules. 

 The growth of the alae is initiated by pollination, progressing 

 far before development of the embryo begins. Fertilization 

 seems to take place about forty to seventy-two hours after 

 pollination. 



Abnormalities in embryosac development were many. It is 

 to be remembered that of the two ovules formed in each cavity 

 of the ovary only one comes to maturity, and that even in the 

 flowers that are developing normally half the embryosacs seen 

 will be in stages of abnormal development or degeneration. 

 The presence of sterile flowers increases the number of atypical 

 cases. The frost mentioned above seemed to destroy the egg 

 first, so that a several-nucleate endosperm with a shriveling egg, 

 as well as other degenerate conditions, was found in material 

 gathered on the days succeeding the cold spell. 



In one ovule of Acer platanoides an embryosac with a double 

 embryo appeared. The second appeared as a smaller individual, 

 attached to the base of the primary one. It possibly resulted 

 from a bifurcation of the head end of the embryo while small, 

 after which one of the halves greatly out-grew the other (Figs. 

 91, 92). 



Seedling Anatomy 



A study of the anatomy of the developing Maple seedling 

 offers little of itself, but a comparison of the normal with a 

 tricotyledonous specimen which sprouted in one of the cul- 

 tures is of interest. The development in maples of specimens 

 with abnormal numbers of cotyledons and of later leaves in 

 whorls of three or even more is well known (15) as is also twin- 

 ning, etc. (5). 



In Acer rubrum the cotyledons have in the contracted lower 

 part of the blade about six vascular strands (Fig. 93). These 

 unite in the petiolar part to two (Figs. 94, 95) which pass un- 

 fused into the hypocotyl (Figs. 95, 96). The plumule at first 



