178 



MEMOIRS OF THE XEW YORK HOTAXICAL GAUDKX 



EXPLANATION OF PLATE 2G 



The reciprocal alternations in the development of sexes as they nor- 

 mally ooenr each day in the two main gronjis of avocados are here well 

 shown. 



Flowers of Taylor, t.ypical of the A varieties, are shown at the right. 

 Flowers of Panchoy, representative of the B varieties, are shown at the 

 left. The upper photo is typical for the forenoon, the lower typical for 

 the afternoon. In each photo the two branches were photographed to- 

 gether at the same moment. 



In the forenoon, on trees of Panchoy, only flowers in the second or 

 male opening are open and on trees of Taylor only flowers in the first 

 or female opening are open. During midday a shift of sets occure in each 

 and then in the afternoon the trees of Taylor become male while those of 

 Panchoy become female. 



The daily sequence of sets of flowers for Taylor is the reverse of that 

 for Panchoy. In general and under nonnal flower action the daily se- 

 quence of sexes in avocados is either as here shown for Panchoy or as for 

 Taylor. The reciprocating alternations of sex provide for cross-pollina- 

 tion between members of the two groups. 



