654 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



the other. While over-rapid growth al- 

 ways tends to lessen the fruitfulness of 

 a tree, lack of food or insufficient nour- 

 ishment will produce the same effect. The 

 remedy in either case is obvious and the 

 condition is readily corrected. 



Diseases Attackiue Bloom and Unfavor- 

 able Weather Conditions 



One of the most frequent causes of 

 failure to set fruit is due to the attack 

 of bloom by fungi. The brown rot of 

 stone fruits and the scab of apple is 

 often responsible for failures which the 

 grower attributes to frost or winter freez- 

 ing. These diseases not only attack and kill 

 the crop of bloom but they may so injure 

 the tree as to prevent the formation of 

 a crop of bloom for the following year. 

 It is probable that many diseases act in 

 an indirect way to prevent fruitfulness. 

 In addition to actual parasitic diseases, 

 unfavorable weather may result in path- 

 ological conditions which prevent a set 

 of fruit; or, on the other hand, they may 

 simply prevent pollination, which has the 

 same result. More than once we have 

 noted a failure in crop due entirely to 

 continued rainfall during the blooming 

 season. 



The effect of winter freezing and frost 

 is largely beyond the control of the grow- 

 er and need not be discussed here. Other 

 minor causes of unfruitfulness might be 

 enumerated, but it is our purpose to dis- 

 cuss only the chief causes in such man- 

 ner as will illustrate the use and value 

 of the bloom charts published below. 

 Probably the chief and most frequent 

 cause of unfruitfulness in orchards is due 

 to self-sterility and the lack of pollen- 

 izers for the self-sterile varieties. 



Self-Sterility and Mixed Plantinar 



Self-sterility may be defined as the in- 

 ability of certain varieties to set fruit 

 when offered only their own pollen. Other 

 minor causes such as imperfect pistils 

 and insufficient supply of pollen may be 

 responsible for sterility in flowers, but 

 such defects are not usuall.v nimierous 

 enough to affect the crop materially. Self- 

 sterility is due to the impotency of the 

 pollen of certain varieties toward its sis- 



terhood of pistil?. This pollen may be 

 quite virile on other flowers but has no 

 affinity for its own. Waite was the first 

 investigator in this country to give this 

 subject close study, and his work has 

 fully demonstrated the fact that many 

 varieties of both pear and apple are either 

 partially or wholly unfruitful when 

 planted in large blocks to themselves. 

 Waite also found that even where self- 

 sterility did not prevail that cross pollina- 

 tion among varieties resulted in better 

 development of fruit. Waugh has made 

 exhaustive studies on this subject so far 

 as it relates to plums and his conclusions 

 are that practically all varieties of native 

 plums and many of the Japanese group 

 are unable to set fruit without the pollen 

 of a second variety. Fletcher has added 

 the further knowledge that self-sterility 

 and self-fertility are not constant varietal 

 characters, but depend to some extent on 

 climatal or other environmental condi- 

 tions. The subsequent studies of many 

 investigators and the general experience 

 of orchard practice confirm these con- 

 clusions; and the majority of well in- 

 formed fruit growers now consider mixed 

 planting a necessity. The practical ques- 

 tion at once arises: What variety shall 

 be selected as pollenizer for any given 

 sort. 



Selection of Pollenizer 



Two factors must be taken into con- 

 sideration in the selection of varieties for 

 cross-pollination. First, there must exist 

 a mutual aflinity between the two; and 

 secondly, they must bloom at practically 

 the same time. 



The subject of mutual aflinity is a very 

 important and interesting one, and has a 

 direct bearing on the whole problem. But, 

 thus far, little is known regarding such 

 afiinities, and the way to further knowl- 

 edge is beset by so many obstacles that 

 few investigators have the courage to un- 

 dertake exhaustive research along this 

 line. We have some knowledge of the 

 subject so far as it relates to different 

 groups of the same fruit, but this knowl- 

 edge should be extended to the relation 

 between varieties of the same group if we 

 are to be in a position to give a definite 



