144 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
may here be said that a complete record of dropped apples is kept ; 
but it is of course impossible to see for certain what proportion of the 
" drops " come from clusters.) 
In spite of this disadvantage, of five varieties for which observa- 
tions of this kind were made in 1921, four showed a considerably 
higher proportion of clustered fruits on the long-spur pruned trees. 
The exception, ' Allington,' is hard to explain ; for Table II. has 
already shown that the percentage of blossom setting was slightly 
higher in 1921 on the long-spur pruned ' Allingtons ' ; and the fruit 
of this variety is moderately long-stemmed, and would not tend to 
be forced off to so great an extent as some of the other four varieties 
concerned — e.g. ' Newton Wonder.' 
The factors influencing the setting of the blossom are undoubtedly 
many and complex. It would perhaps be hardly correct to say that 
pruning appears to be one of them, but rather that the pruning has 
indirectly affected the setting of the blossom by influencing one of 
the direct factors. If we call this factor " vigour," while we may not 
gain anything in actual knowledge (since we have as yet no satis- 
factory measure of " vigour "), the idea is at least suggestive, and 
leads to certain deductions of considerable importance to the pruner. 
The first of these is closely in accordance with the practice of some 
of the best growers. If a certain minimum vigour is necessary to 
the setting of enough blossom to produce a crop, the failure of many 
old weak or stunted trees to crop, although they blossom freely, may 
clearly be due to their weakness. It is known that a moderate 
" heading back " of the branches, coupled with suitable soil treatment, 
will often restore such trees to a profitable condition. 
A second consideration is at present too speculative to be more 
than mentioned. There are indications that of the long-spur pruned 
trees of certain varieties the weaker trees set a larger proportion of 
their blossom than the stronger ; in other words, that there is an 
" optimum " vigour for setting. (The only measures of vigour avail- 
able are size of tree and weight of prunings.) This, if it should prove 
to be a fact, will clearly affect the details of pruning methods very 
closely. Careful observation suggests that the too hasty cutting back 
of a spur, formed by shortening a lateral, to a fruit bud, may lead to 
the failure of the fruit bud to set fruit, and a consequent vigorous 
formation of wood growth which may delay the formation of the 
spur. Much more observation is needed before this point can be 
cleared up. 
3. Effect on Cropping. 
(a) Number of Fruits. — The number of fruits borne by a tree 
follows directly, of course, from the number of blossoms and the 
proportion of them which sets. In spite of the usually much higher 
percentage of blossom which sets on the long-spur pruned trees, they 
have, in^every case except two, been considerably delayed in cropping 
