Study of Reproduction in the Genus Acer 1 13 



The thirteen chromosomes thus formed divide equally and there 

 is found no basis in an unequal division for a differentiation 

 into male or female determining individuals. But Darling con- 

 siders that in the reorganization of the nuclei in the tetrad two of 

 the nuclei contain each a chromatin body lacking in the other 

 two, and that this feature may be related to sex determination. 

 The body in question seems to disappear soon after, during the 

 passage into the resting state. 



The unusual conditions represented by this author as present 

 in Acer negundo were denied in a subsequent work by D. M. 

 Mottier on the same species, published in 1914 (13). Here a 

 very clear and convincing account is given of the conditions 

 present and a comparison made with the somewhat related 

 Staphylea trifolia L. He also, besides giving a more normal 

 history as that typical of the maple, disputes the correctness of 

 the count, giving twelve as the probable number in one place, 

 and in another suggesting either twelve or fourteen. Mottier 

 incidentally gives the chromosome count in Acer rubrum as 

 thirty-six in the reduced condition. In an earlier paper (12) 

 he describes the mature pollen of this species. 



With regard to the ovule development, the only paper avail- 

 able is that of Mottier on Acer rubrum, 1893 (12). He reports 

 that late in March the megaspore mother-cell is evident as a 

 sub-epidermal cell, which becomes more deeply placed by later 

 divisions of the nucellar epidermis. Its first appearance was not 

 determined. The first division in the mother-cell is followed by 

 wall formation, and then the more micropylar of these again 

 divides with a resulting wall. Both these cells degenerate. 

 The more chalazal of the original pair divides later than the other, 

 but no wall is laid down, and the embryosac by two additional 

 successive divisions reaches the eight-nucleate stage. The three 

 antipodals early disappear after maturity, and the polar nuclei 

 fuse preliminary to fertilization. 



Material and Methods 



The writer was fortunate in being able to obtain material of 

 a considerable number of species, both native and exotic in ori- 

 gin. The greater part of the exotic material could not be worked 

 up with thoroughness, and so will not be considered in this paper. 

 Buds of Acer platanoides L. and Acer rubrum L. were made avail- 



