FLORIDA STATE HORTICULTURAL SOCIETY 



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after opening on the plant, so there is 

 a chance for insects to carry pollen from 

 flower to flower on a plant or from plant 

 to plant of one clonal variety. There is, 

 hence, a pollination problem and the ac- 

 tion of insects is necessary to effect pol- 

 lination, but the growing of a clonal va- 

 riety does not make it the more difficult. 

 In most fruit crops, Apple, Pear, Peach, 

 etc., there is a partial dichogamy, but the 

 pistil of a flower, as a rule, remains ready 

 for pollination until after the pollen is 

 shed from some of the anthers of the 

 flower, so there is opportunity for self- 

 pollination. Also in these fruits there are 

 flowers of all stages of development open 

 at the same time during most of the pe- 

 riod of bloom, so there is abundant op- 

 portunity for close-ipollination by action 

 of insects. As far as pollination is con- 

 cerned the clonal variety of such a plant 

 may be planted in solid blocks. 



But dichogamy may be so highly spe- 

 cialized that close-pollination is also re- 

 stricted, as is the case with Avocados. In 

 this plant the flowers are perfect, but each 

 flower has normally two distinct periods 

 of opening. The pistil of a flower is 

 ready for pollination at the first time the 

 flower opens, but it is only during the 

 second period of opening, at least 14 hours 

 later, that the pollen is shed. This pre- 

 vents self-pollination. But the flowers 

 of a tree, or of trees of a clonal variety, 

 open and close together for each of the 

 two periods of opening. Flowers of a 

 kind in the same period "flock together" 

 and this daily rhythmic synchrony restricts 

 close-pollination. It will readily be seen 

 that if all Avocados (seedlings, clonal va- 

 rieties, etc.,) have the same daily se- 



quence, cross-pollination among Avoca- 

 dos would likewise be restricted. But a 

 survey of the varieties shows two main 

 types of daily sequence. In one group of 

 varieties pollen is shed in the forenoon and 

 first-period flowers ready for pollination 

 are open in the afternoon. In the other 

 group the behavior of flowers is in the re- 

 verse order. The two types supplement 

 each other. The time relations are won- 

 derfully adapted for cross-pollination be- 

 tween individuals of the two groups. 

 Solid block plantings of a clonal variety or 

 mixed planting of varieties that have the 

 same daily sequence of bloom will de- 

 crease the chances for pollination. The 

 Avocado is a conspicuous case showing 

 that the flower behavior of a new type of 

 fruit crop and its requirements for polli- 

 nation should always be determined be- 

 fore clonal varieties are planted in solid 

 blocks. 



WHEN SELF- AND CLOSE-POLLINATIONS 

 DO NOT RESULT IN FRUIT 



Self-fruitlessness exists in such clonal 

 varieties as the Napoleon Cherry, the 

 Bartlett Pear, the German Prune Plum 

 and the Rhode Island Greening Apple and 

 in many other varieties of these fruits. 

 Each of these has perfect flowers with sta- 

 mens fully developed and with pollen 

 highly potent. Each is known to be ca- 

 pable of yielding heavy crops of fruit. 

 There are no marked differences in the 

 time of the development of the pistils and 

 stamens of the individual flowers. The 

 flower mechanism does not prohibit self- 

 pollination even without insect visita- 

 tions, but with such visitations close-pol- 

 lination is amply provided for. And yet 



