THE FLOWER BEHAVIOR OF AVOCADOS 



161 



Evidence bearing on the evolution of dianthesis and 

 synchronous dichogamy in avocados 



The flower behavior of avocados exhibits an advance in de- 

 velopment beyond the dichog-amy generally seen in other plants 

 in at least three important particulars. 



First there is a definite and pronounced interval between two 

 distinct openings of each flower. Except for general periodic 

 closing such as night closings, the dichogamous flowers of other 

 species (as far as known) have one continuous period of open- 

 ing and the flowers have what amounts to a single opening. 



This is closely approached or perhaps realized in certain of 

 the B varieties which have the shortest cycle in the action of sets 

 of flowers (see chart 5) and in which the interval of closing is 

 for one night only. From this rather simple and short cycle the 

 complexity increases to cycles having longer intervals, giving 

 flowering cycles of 36 hours and 48 hours. 



Furthermore, certain changes in temperature may cause 

 flowers or sets of flowers to skip the first opening and to open 

 only for a single oi^ening. x\nd the varieties with the shortest 

 interval are most liable to behave thus. All this may be taken as 

 evidence that the extended cycle of the avocado flower with its 

 two periods of opening has evolved from a simpler cycle of only 

 one anthesis. A study of flower behavior in the close relatives of 

 the avocados may reveal evidence on this matter. 



So far as is known, in other 2:)lants dichogamy is not exclu- 

 sively synchronous for the entire plant. For certain species hav- 

 ing monoecious flowers, there is a tendency for female flowers to 

 ripen before the male flowers, giving somewhat of a seasonal 

 alternation in the sex of the entire plant. In pecans, for ex- 

 ample (see Bulletin No. 124, Georgia Experiment Station, by 

 H. P. Stuckey) this condition is so fully developed for certain 

 clonal varieties that they are decidedly self-fruitless. But for 

 plants with perfect but dichogamous flowers the rule is that some 

 flowers will be shedding pollen while others are ready for pollin- 

 ation. Unless there be but one flower open at a time there is 

 chance for close-pollination. For avocados this condition is 

 frequently seen when there is overlap of sets during off-stride 



