H2 Taylor — A Morphological and Cytological 



LIHR- 1 

 BOTANICAL 



Introduction qa kuB 



At the inception of this work the writer planned to review the 

 genus Acer from the standpoint of the evolutionary tendencies 

 shown by the comparative morphology of the floral parts, as well 

 as the relative degrees of dicecism and flowering periods of the 

 different species. A preliminary survey of the available sources 

 of material and information showed that it would be imprac- 

 ticable to secure sufficient data to insure a comprehensive view 

 of all of the sub-genera. This was especially true with respect 

 to living material. On the other hand, the literature regarding 

 the development of the reproductive elements was found to be 

 very meagre, and in some particulars, contradictory. Since as 

 many species as could be handled in a cytological study were 

 within reach, an attempt to clear up the points in dispute and 

 to extend our knowledge of the genus to unstudied species led 

 to the abandonment of the original problem. 



Historical 



The first paper to appear dealing with the cytology of Acer 

 was by Ira D. Cardiff in 1906 (2). This was primarily a study 

 of synapsis and the organization of the heterotypic chromosomes, 

 presenting the viewpoint of parallel pre-synaptic threads and 

 paired chromomeres. He worked with Acer platanoides and sev- 

 eral other plants of widely differing groups, describing an essen- 

 tial similarity of behavior throughout. The reduced chromo- 

 some number for the maple considered is given as eleven. 



This work was followed by a study of Acer negundo by Chester 

 A. Darling in 1909 (4), an effort to determine the basis for the 

 dioecious condition in this form. The whole history of the 

 maturation divisions as described by this author is at variance 

 with the usual process of pollen development. The chromatin 

 is said to leave the nucleolus during the presynaptic phases in 

 the form of round bodies which build up the spireme on the 

 linin threads. Later the spireme breaks up to form eight 

 bivalent chromosome segments, while from the nucleolus bud 

 off directly five more bivalents. Upon the breakdown of the 

 nuclear membrane what is left of the nucleolus is said to divide 

 up into a few granules which pass out from the spindle region. 



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