POLLINATING FRUIT TREES 
Many Problems Connected with Failure of Trees to Set Crop—Must Be Worked 
Out by Experiment—Results of Some Long-Continued Trials in England 
LESLIE GORDON CORRIE 
Queensland Acclimatisation Society, Lawnton, Queensland, Australia‘ 
the chief purpose of a conspicuous 
flower is to attract insects, which 
may act as the agents in transferring 
pollen from another individual. Fail- 
ing, however, the arrival of any foreign 
pollen, many flowers are able to set 
seed with their own pollen and in fact 
many flowers are provided with various 
elaborate contrivances, to effect self- 
pollination, should cross-pollination fail. 
There are, however, a large number of 
plants, which, even when carefully self- 
pollinated, are quite unable to set seed 
or develop fruit with their own pollen. 
To this set belong many of our 
common wild plants, and many of our 
cultivated plants, too; but what con- 
cerns the fruit grower most is that 
many, if not the majority, of our com- 
mon fruit trees are in this category. 
It has frequently been observed by 
practical men that large blocks of 
only one variety of apple or pear have 
fruited badly, except in the outside 
rows; others have contended that large 
blocks of one variety have fruited well 
all through. Both may be correct, and 
a good deal of the explanation depends 
upon a clear conception of the meaning 
of the term self-sterile. A plant is said 
to be self-sterile when it fails to set 
seed with its own pollen, though this 
same pollen may be perfectly potent on 
another variety. This should not be 
confused with such cases as occur in 
the gooseberry and the currant, where, 
though the flowers are perfectly self- 
fertile, fruit is but rarely if ever set, if 
the visits of insects are excluded; here 
it is chiefly a mechanical difficulty, as 
the stamens bearing the pollen are 
|: HAS long been recognized that 
situated in such a position that they 
cannot come in contact with the stigma, 
the female organ; and, further, the pollen 
is of a glutinous nature. The practical 
difference is that, whereas in this latter 
case a supply of bees would ensure a 
crop of fruit, even if only one variety 
be grown, in the former no number of 
bees would make any difference. 
FRUITS WITHOUT SEEDS 
There are some varieties of apples 
and pears which will set fruit on being 
self-pollinated, but these fruits do not 
contain any real seeds; such fruits are 
of course more or less satisfactory to the 
fruit grower who wants fruit. This 
also occurs in some varieties of goose- 
berries; such berries are, however, de- 
cidedly lighter in weight than those 
containing seed, and are therefore 
obviously of less value to the grower; 
the apples without seed, also, are often 
inferior both in size and shape. 
In plums and cherries these par- 
thenocarpic fruits do not occur, at 
least not to any appreciable extent; 
an occasional fruit may be found with a 
shrivelled kernel, but I have noticed 
that, as a rule, if this shrivelling takes 
place before the fruit is well developed 
it falls, and I think that it is probably 
due to imperfect fertilisation. 
_ Plums seem to be fairly equally 
divided between self-fertile and self- 
sterile varieties, and there are a few 
which cannot be directly classified as 
one or the other. In apples and cher- 
ries, self-fertile varieties appear to be 
greatly in the minority. Through ex- 
periments carried out chiefly on pot 
trees at the John Innes Horticultural 
1 Mr. Corrie was formerly connected with the John Innes Horticultural Institution at Merton, 
Surrey, England, of which William Bateson is director. 
With this article the reader should compare ‘‘The Self-Sterility Prob- 
lated at that institution. 
The data here presented were accumu- 
lem” by E. J. Kraus, in JoURNAL oF HeErReEpITy, VI, 12, pp. 549-557, December, 1915.—THE 
EpITor. 
365 
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