146 



MEMOIRS or THE NEW YORK BOTANICAL GAIiDEX 



same day. This alternation of the sexes for the entire tree con- 

 tinues day after day with a re<:!,'nlarity that greatly limits or even 

 entirely prevents both the self-pollination of individual flowers 

 and pollination from one flower to another (close-pollination) on 

 the same tree or on different trees of the same clonal variety. 



But what is still more remarkable, certain plants (individual 

 seedlings and clonal varieties as such) are female during the 

 hours of the day when other plants are male and then there is a 

 reversal of sex in each for other hours of that same day. These 

 reciprocating changes in sex provide chances for mutual cross- 

 IDollination between certain plants. 



The flowers are perfect, relatively simple, and very uniform 

 in structure throughout the species or group of species repre- 

 sented in the cultivated avocados. The adaptation for cross-pol- 

 lination is accomplished by physiological regulation. The daily 

 rhythmic alternation of sexes (synchronous dichogamy) for the 

 entire jilant and the reciprocation of these changes in certain 

 groups of plants reach a jjerfection of physiological regulation 

 in avocados that is unapproached, as far as is now known, in any 

 other grouiD of plants. 



HOAV SYNCHRONOUS DICHOGAMY IS ACHIEVED IN AVOCADOS 



The manner in which synchronous dichogamy is accomplished 

 in avocados may be explained by tracing the events in the be- 

 havior of the flowers of a single tree throughout an entire day 

 during a period of favorable weather. For this purpose a tree 

 of the Taylor variety (a clonal variety) may be selected. 



In the hours of early morning no flowers are open anwhere 

 on the tree but during the early forenoon flowers begin to open 

 here and there in the various clusters of flower buds all over the 

 tree. In the opening of a flower, the six leaf -like segments of the 

 perianth separate and bend outward. The tAvo sets of six outer 

 and three inner stamens follow and when the flower is fully 

 oj^en these stand nearly at right angles to the main axis of the 

 pistil as seen in the open flowers shown in plate 24. This leaves 

 the pistil standing erect, alone, conspicuous and fully exposed, 

 with the slightly enlarged end (the stigma) white, fresh and soon 



