162 



MEMOIRS OF THE ^'E\V YORK BOTANICAL GAKDEIf 



and irregular behavior. The ease witli Avliicli this occurs may 

 indicate that this Avas the general condition from which evolved 

 the perfection in the daily and synchronous alternation of sexes 

 now seen in avocados. 



In avocados the climax in the adaptation of dichogamy for 

 cross-pollination is seen in the reciprocation of the daily se- 

 Cjuence. Nothing approaching this condition is known for any 

 other group of plants. There are two classes of individuals, ap- 

 parently nearly equal in number, and the daily sequence of one 

 is the reverse of the other. This indicates an inherent organiza- 

 tion with hereditary values and determination. 



But the precise behavior is far from uniform among the indi- 

 viduals of either group. In respect to time of the opening of 

 flowers, the duration of the periods of opening, the length of the 

 interval and the period of overlap, there are wide differences 

 characteristic of individual seedlings and clonal varieties. 



When the behavior of varieties is arranged in sequence for 

 the time of tirst opening there are many gradations from the 

 earliest of the A varieties to the latest of the B varieties (see 

 CHARTS 1 to 4). The hereditary basis involved in the differentia- 

 tion of the two groups can scarcely be considered as due to a 

 few simple units of uniform value and as achieved in one step by 

 a single change in heredity. 



The MALE STERILITY OF THE CoLLINSOX VARIETY^ 



The Collinson variety is an excejition among cultivated varie- 

 ties of avocados in that it is completely sterile as a pollen parent. 

 The flowers have two periods of opening and the second opening 

 is normally in the afternoon but the anthers remain closed and 

 no pollen is shed (see in plate 27). Sections properly prepared 

 for microscopic study reveal that the stamens are mere masses 

 of sterile tissue. 



The writer has made observations on the floA\^rs of the 

 original tree of the Collinson (a seedling from open-pollinated 

 fruit collected at the Miami Station for Plant Introduction), of 



1 The writer did not see any trees of this variety in California. ' The facts regard- 

 ing the male sterility of Collinson were first determined in 1925 through the joint 

 observations of Mr. E. M. Savage and the writer. 



