Study of Reproduction in the Genus Acer 123 



In Acer platanoides the reduced number of chromosomes is 

 given by Cardiff (2) as eleven. This the writer has been able 

 to confirm, although the amount of material available was not 

 great (Figs. 59-62). The seeds of this species were germinated 

 and the root tips fixed to verify this by making a 2x count. 

 Here a word must be recorded with regard to the conditions of 

 observation of the mitoses, especially the somatic ones. In all 

 of the maples studied the chromosomes in the vegetative parts 

 are very small indeed. The longest studied measures about 

 three microns in length and the smallest about one micron, 

 with in both cases a diameter of from two-thirds to one-third 

 micron. Even with good fixation, which with the roots was 

 consistently obtained, overlapping of the ends of these bodies, 

 and other confusing arrangements frequently occurred. This 

 made the interpretation of the complex plates a difficult matter, 

 and in the extreme cases of Acer rubrum and an abnormality 

 under Acer saccharinum, compels the count arrived at to be 

 considered merely as a very careful approximation. The method 

 pursued in making all the chromosome counts, both somatic 

 and gametophytic, was to draw the most perfect plates with the 

 camera lucida at a magnification of 3380 diameters, correct the 

 rough sketch by direct observation and recompare under the 

 camera before counting. This enabled the writer to be sure no 

 element had passed by unobserved. In the cases of small ix 

 plates, a few actual drawings were supported by many direct 

 observations, readilv made when a small number of elements 

 was concerned. With Acer platanoides, having the smallest 

 number of chromosomes yet observed in the genus, it was a 

 surprise to find that the somatic count obtained in the root tip 

 cells did not agree with the reduced count, for the number 

 twenty-six was persistently obtained (Figs. 57, 58). A very 

 few counts of twenty-five, twenty-seven and twenty-eight prob- 

 ably contain observational errors. The difference between the 

 observed number and that of twenty- two which was expected, 

 is too great to be an error, and indicates probably that there 

 exist varieties differing in cytological composition. As no sys- 

 tematic attempt was made to keep records of the exact trees 

 furnishing the material for each fixation, these features unfor- 

 tunately cannot be correlated with the horticultural forms and 

 varieties listed by Pax (14). A further feature of this kind 

 appeared and will be considered under Acer rubrum. 



