THE ANNONACEOUS FRUITS 173 



however, he was able to obtain thirty-six fruits from forty-five 

 flowers. 



After carrying on pollination experiments in Florida during 

 several years, P. J. Wester 1 wrote: "The investigations indi- 

 cate that the flowers of the cherimoya, the sugar-apple, the 

 custard-apple and the pond-apple are proterogynous and 

 entomophilous, though the pollinating agent of the last-named 

 species has not been detected." A proterogynous plant, it may 

 be remarked, is one in which the pistils are receptive before 

 the anthers have developed ripe pollen, cross-pollination being 

 therefore necessary, and some outside agency being required 

 to effect it. In the case of the annonas the work is done by 

 insects ; hence the plants are termed entomophilous. 



The pollination of the closely allied Asimina triloba is 

 thus described by Delpino : 2 " The stamens project in the 

 center of the pendulous protogynous (proterogynous) flower as 

 a hemispherical mass, from the middle of which a few styles 

 with their stigmas project. In the first (female) stage of 

 anthesis the three inner petals lie so close to the stamens that 

 insect visitors (flies) cannot suck the nectar secreted at the 

 bases of the former without touching the already mature 

 stigmas. In the second (male) stage the stigmas have dried 

 up and the inner petals have raised themselves, so that the 

 anthers, now covered with pollen, are touched by insects 

 on their way to the nectar. Cross-pollination of the younger 

 flowers is therefore effected by transference from the older ones." 



Wester concluded that one cause of the unproductiveness of 

 the cherimoya in Florida was the scarcity of pollinating insects. 

 Even under the same conditions of environment, however, 

 there are marked differences in productiveness among seedling 

 trees. The subject deserves further investigation. Produc- 

 tive varieties especially should be studied, to determine whether 



1 Bull, of the Torrey Bot. Club, 37, 1910. 



2 Paul Knuth, Handbook of Flower Pollination. 



