154 



MEMOIRS OY THE NEW YORK BOTANICAL GARDEN 



For certain B varieties the rule is for each set to open for the 

 second time during the next forenoon after an interval of about 

 12 hours. For such sets the complete cycle is about 24 hours. 

 In this case but one set is in some stage of the cycle at a time 

 (see Bl in chart 5) and it completes its flowering cycle alone and 

 while every other set is inactive. The studies indicate that this 

 behavior is characteristic of certain West Indian varieties of 

 which TrapjD may be mentioned as fairly tj^pical. In Florida in 

 1925 the weather during February and March was unusually 

 warm and the 24-hour cycle was usual for sets of flowers on 

 many of the B varieties. 



For certain of the B varieties, however, sets of flowers open- 

 ing for the first time in the afternoon may remain closed for two 

 nights and one day (of daylight). The interval between the two 

 openings is 36 hours and the entire cycle covers 48 hours as 

 shown in B 2 of chart 5. Under such behavior three different 

 sets of flowers, including the set in the interval, are in some stage 

 of action during each period of daylight. During the hours of 

 darkness two different sets are in the interval. In California, 

 throughout nearly all of the period of study in 1923, this was the 

 regular rule of sequence for B varieties under observation when 

 there was a normal daily alternation. The nights were, how- 

 ever, much cooler than in Florida. Nothing like the Florida con- 

 ditions of March 1925 were experienced in California in 1923 

 wjiere studies were made, until very late in May when the bloom- 

 ing of avocados was mostly over. 



On trees of certain varieties the cycle of sets of flowers may 

 shift from 48 to 24 hours, or vice versa in response to certain 

 changes in weather. It is to be noted, however, that at times 

 when the 48-hour schedule gives normal daily alternation of two 

 sets for these varieties, certain other varieties of the B group, 

 such as Trapp, may be blooming on the 24-hour schedule. None 

 of the tender AVest Indian varieties which in Florida rather per- 

 sistently bloom on the 24-hour cycle were available to the writer 

 for study in California. 



It was frequently observed, especially of the Harmon and 

 Fuerte varieties, that a single set of flowers opening and closing 

 in unison for the first period will divide into two groups; jiart of 



