Study of Reproduction in the Genus Acer 125 



negundo. He there gives the reduced chromosome count for 

 Acer rubrum as thirty-six, the same as Staphylea. This marked 

 the form as strikingly different in nuclear composition from the 

 others then known, Acer negundo and Acer platanoides. It was 

 early examined by the writer for comparison with the others, 

 but the number of chromosomes was so large that with the poor 

 fh ation at first obtained, it seemed impossible to obtain a count. 

 With later material better success was attained, and the number 

 determined as being between sixty-eight and seventy-five (Figs. 

 30, 79-81). This is about twice the number given by Mottier. 

 It was not till material of the reduction divisions in the mega- 

 spore mother cell was studied that the original count of thirty- 

 six was seen (Fig. 34) by the writer. Here a few late prophases 

 gave results approximately verifying Mottier. The megaspore 

 metaphases were not in such a position that they could be 

 counted. This gives a very interesting situation, since the 

 pollen material first studied clearly represented a race with a 

 2x gametophytic count. As proof of two cytologically distinct 

 lines of Acer rubrum this evidence is far more decisive than that 

 for Acer platanoides. To add to the interest of the situation 

 some material belonging to two other batches was found, which, 

 though not as good as that from which the 2x gametophyte 

 count was obtained, showed clearly that the reduced number 

 of the chromosomes was here in the neighborhood of fifty (Figs. 

 82-84). If the original number of thirty-six is exactly correct, 

 which, although it seems probable, the writer would not under- 

 take to absolutely affirm with the few data at his disposal, 

 then seventy-two would be the expected reduced number in the 

 tetraploid form. 



The pollen of the material above described probably repre- 

 sents such a race. If these hybridized, then the pollen of the 

 hybrid form would have a count of fifty-four according to ordi- 

 nary expectations, which was observed in one instance in the 

 two fixations just mentioned, although most of the counts run 

 from fifty to fifty-two. The seventy-two chromosome class of 

 pollen was found in pollen of male flowers, the apparently "hy- 

 brid" condition in the pollen of both male and female flowers. 

 Unfortunately, such a situation being totally unforseen, no 

 records are to be had that would locate the original trees. Meas- 

 urements were made to compare the size of the microspore 



