126 Taylor — A Morphological and Cytological 



mother cells at the first metaphase. The longest and shortest 

 diameters of each grain were taken and averaged for the series. 

 The tetraploid material gave an average diameter for those 

 counted of 29 microns, the pollen from the "hybrid" male 

 flowers gave 23.5 microns, and the pollen from the female "hy- 

 brid" 24.8 microns. The difference between these last two is 

 hardly significant, being probably a shrinkage variation. The 

 volume of the tetraploid cells is therefore about 12,800 cubic 

 microns each, and that of the larger "hybrid" material about 

 8,000 cubic microns, which gives a ratio somewhat less than 

 that of the chromosome numbers, namely 4:2.5 as against 4:3. 

 Abnormalities in pollen formation have appeared in Acer 

 rubrum, which may throw light on the origin of these conditions. 

 In the material giving the intermediate count, one case of a tri- 

 polar spindle was found, with the chromosomes partlv oriented 

 with respect to one axis, partly with respect to the others. In 

 different material pollen grains were found of two sizes inter- 

 mixed, in diameter about 39 and 27 microns respectively. Fur- 

 thermore, conditions of lack of complete separation of the orig- 

 inal tetrad were found, both where, within the wall of the mother 

 cell, each of the four had formed a wall of its own and also where 

 they remained naked within the common investment. These 

 were in anthers where the majority of the pollen grains were 

 well advanced toward maturity. Some large grains were present 

 with abnormal numbers of nuclei. Germination of the seeds of 

 the Red Maple furnished material for a study of the somatic 

 divisions, but the extreme complexity of the figures made the 

 counting too much of a strain, and, since the accuracy was com- 

 parative at best, only a few cases were critically studied. The 

 number of chromosomes as counted seemed to be above ninety 

 (Figs. 76-78). Owing to the conditions mentioned it would 

 be unwise to try to interpret this in terms of the reduced number. 



Ovule Development 



The only maple which has received attention with respect to 

 the development of the ovule and embryosac is Acer rubrum, 

 upon which Mottier published a paper in 1893 (12). This paper 

 was written before some of the most important advances in 

 methods of technic, and it was thought advantageous to follow 

 the development again in the same species. The observations 



