Just under seventy years ago, Crane and Lawrence did some work on apple pollination. They found, by experiment, the percentage of apples maturing from self-pollinated and cross-pollinated trees.
We all know that if you have a triploid tree (e.g. Bramley, Ribston or Blenheim), the crop will often be poor if it stands on its own. For those who are interested, here are the figures they published in 1938: apples maturing per 100 flowers pollinated. T denotes triploid. In these experiments they didn't actually cross-pollinate any triploids, but you can see from the figures that triploid self-pollination isn't the only problem; when it comes to self-pollination, most diploids are worse.
There isn't much comment necessary here, other than to point out the rather obvious conclusion that choosing incompatible trees will severely affect the amount of fruit you get; perhaps by a factor of four or five if the combination is particularly bad. I was surprised by these figures in two ways... I thought triploids would set no fruit on their own; this is incorrect. I also thought Cox was self-fertile, but the figures show it to be less productive than Bramley, Ribston or Blenheim when self-pollinated.....
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