n6 Taylor — A Morphological and Cytological 



Acer negundo follows a week or ten days later than Acer rubrum, 

 and maturation of the pollen also occurs during the opening of 

 the buds. In these three forms, with relatively condensed in- 

 floresences it might be expected that in any given bud the stages 

 would be almost simultaneous, but a great variation, even in 

 the lobes of a single anther, was the regular condition. The 

 same holds true for Acer saccharum, which blooms a little later 

 than Acer negundo. 



It is, however, in the forms with a more complex inflorescence 

 that this variation in the time of development reaches the great- 

 est degree. Acer platanoides, the next of the common forms 

 to open, will show any condition from mature archesporium 

 to young pollen grains in the same flower cluster. This renders 

 the accumulation of a considerable quantity of material of any 

 one stage rather a prolonged task. Maturation occurs during 

 the swelling of the bud, and by the time the scales have opened, 

 most of the anthers will contain pollen grains. The time for the 

 actual flowering of this species is generally the second week in 

 April. Acer pseudo-platanus has the largest flower mass of any 

 of the commonly grown species, and here development proceeds 

 from the base of the raceme toward the tip, with great secondary 

 differences in the stage of development of the flowers on the 

 secondary racemes. The reduction divisions take place largely 

 while the racemes are from 10-15 mm. in length. It flowers 

 soon after Acer platanoides. Data for the Japanese and the 

 more rarely cultivated European species are incomplete, but 

 they mostly flower, in this region, during April or early May. 



It proved much more difficult to get information with regard 

 to the time at which the reduction divisions take place in the 

 megaspore mother cell. In general it was found that in a flower 

 with young microspore tetrads, the megaspore first prophases 

 were taking place, while the later phases followed the separation 

 of the tetrad. 



Abnormalities in floral structure were not especially sought, 

 but some few appeared. With regard to the constancy of the 

 dioecious condition in Acer saccharinum and Acer rubrum it 

 should be noted that trees of both species bearing alike male 

 and female flowers were found. The flowers occurred in differ- 

 ent infloresences on the same twig in Acer saccharinum. Pre- 

 dominately male clusters of Acer platanoides often bore a few 



