THE PLUMS OF NEW YORK. Ill 



Domestica and Triflora plums are self-sterile and yet the question is an 

 open one as regards some varieties of these species. 



There is great difference in the quantity of pollen produced by the 

 several groups of plxims but it is very doubtful if insufficiency of pollen 

 is a factor of any considerable importance in the self -sterility of this fruit. 

 Yet the matter is worth attention because of its bearing upon the selection 

 of pollinizers. Of the several botanic groups, speaking somewhat generally, 

 the Americanas and Nigras bear most pollen ; the Munsoniana plums are 

 abundant pollen bearers; the Trifloras seldom show a shortage but bear 

 rather less than the others named; the Domesticas produce pollen abun- 

 dantly ; while the hybrid groups are the most capricious of all the plums 

 in this respect, some varieties bearing much and others but little pollen. 

 Probably the amount of pollen which the flowers of any tree produce 

 is somewhat modified by the climate in which the tree is growing, by the 

 weather and by the vigor of the tree. 



Waugh ' and Goff ' have shown that self -sterile pltims often have 

 abnormal pistils or pistils too weak for the development of fruits. Not 

 infrequently flowers of the plum are without pistils, as occasionally, but 

 less rarely, occurs with the stamens and petals. These abnormalities 

 cannot be very general causes of self -sterility in plums, however, as varie- 

 ties, or even trees, cannot often be fotmd which are not fruitful if other 

 varieties are growing near them. It is very doubtful if even so much 

 as fifty per ct. of abnormal flowers, seriously jeopardizes a pliim crop, 

 as the trees bear, if they blossom at all, several times as many flowers as 

 they can mature plums. But a high percentage of abnormal flowers nearly 

 always indicates a general weakness in fruit -setting. 



Another cause often assigned for the failure of plums to set fruit is 

 the difference in time of maturity of stamens and pistils. It is claimed 

 that when these organs do not mature simultaneously the plums do not 

 set unless pollen is supplied from some other source. The task of taking 

 notes at blossoming time on more than three hundred varieties of plums 

 on the grounds of this Station has given abundant opportunity to observe 

 the comparative degrees of maturity of pistils and stamens in varieties 

 of this fruit. In general the pistils mature first, often three or four days 

 before the stamens. Rarely the pollen is disgorged before the stigmas are 

 receptive. But stigmas remain receptive, weather conditions being favor- 



' Waugh, F. A. Vt. Sta. Bui. 53:51. 1896. 

 'Goff, E. S. Wis. Sta. An. Rpt. 18:302. 1901. 



