654 
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 Attacking 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 Planting 
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 usually numerous 
enough to affect the crop materially. Self- 
sterility is due to the impotency of the 
pollen of certain varieties toward its sis- 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
terhood of pistils This pollen may be 
quite virile on othe: 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 tact 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 1esulted 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 affinity between the two; and 
secondly, they must bloom at practically 
the same time. 
The subject of mutual affinity is a very 
important and interesting one, and has a 
direct bearing on the whole problem. But, 
thus far, little is known regarding such 
affinities, 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 
