THE FLOWEK BEHAVIOK OF AVOCADOS 



149 



second or male opening on the afternoon of the following day. 

 There are two distinct and separate periods of anthesis, a con- 

 dition which may be designated as diantJiesis. Between the two 

 periods of opening the set is closed for an interval of about 

 twenty-four hours and the entire time from the beginning of the 

 first opening to the end of the second opening (the cycle of di- 

 anthesis of the set) covers slightly less than thirty-six hours. 



The sequence of sets continues regularly under favorable 

 weather conditions and brings two different sets into opening 

 each day. The forenoon set is open for the first or female open- 

 ing and will open again on the afternoon of the following day to 

 shed pollen. The afternoon set has had the first opening during 

 the forenoon of the day before. Each flower is perfect, it has two 

 distinct j^eriods of being open, it is female during the first open- 

 ing and male during the second opening. The physiological reg- 

 ulation is seen first in the development of the two sexes in each 

 flower at different times (dichogamy) and second in the coordi- 

 nation of this development among entire sets of flowers so that 

 the dichogamy is synchronous for the tree as a whole. 



The two types of daha* sequence in the alternation 



OF sexes 



A general survey of many seedlings and many named clonal 

 varieties of avocados, including Guatemalan, Mexican, and West 

 Indian types and hybrids between these, growing in California 

 and in Florida, indicates that they may all be grouped into two 

 main classes with respect to the daily changes of sex in the 

 flowers. About half of them behave similarly to the trees of the 

 Taylor variety described above and these may be grouped to- 

 gether and designated as Class A. In the other group of seed- 

 lings and varieties (Class B) the secpience in the daily alterna- 

 tion of two sets of flowers is the reverse of that of Class A. For 

 these the second-period or male opening of sets of flowers is, 

 normally, in the forenoon, and their first-period or female open- 

 ing is in the afternoon. 



The relative flower behavior of the two groups may be shown 

 by comparing flowers of two varieties such as Taylor and 

 Panchoy. 



