20 SCIENCE AND FRUIT GROWING 



estimate under ordinarily favourable conditions, the crops from 

 a hundred trees in a plantation of Bramley's Seedling in 1909 

 may be taken ; these trees were on the paradise stock, and were 

 eighteen years old at the time. They bore from 2j to 6 bushels 

 per tree. Taking the weight of crop, and comparing together 

 only such trees as were under similar treatment, it was found 

 that the average difference between the crops of any individual 

 tree and the mean of the trees in the whole plot was 24 per cent. ; 

 this would give the " probable " error (using the term in its mathe- 

 matical sense) of the mean results deduced from a plot of six trees 

 as being Jb 7*i per cent., or I7'5 per cent, for that of the results 

 of a single tree. 



Such a variation, it must be remembered, applies only to trees 

 in contiguous positions, and a considerably greater variation 

 would generally occur in similar experimental plots, if these were 

 situated in distant parts even of the same field : but it must also 

 be remembered that no conclusions would be likely to be based 

 on the crops of a single season only. 



As to the measurement of a tree when no crops are available 

 for estimating the results, or when growth or vigour have alone 

 to be studied, a considerable number of methods have been 

 adopted. The most certain one was to ascertain the increase in 

 weight of the whole tree ; but that could only be done when the 

 experiment was not to be continued for more than a few years : 

 in other cases, yearly measurements of some portion of the tree 

 were made. These consisted of measurements of the general 

 size of tree, taking the mean of its height, spread of branches, and 

 girth of stem at some selected distance above the ground : the 

 weight of the prunings (when the trees were all pruned in the same 

 way) ; the length of new shoots formed, and, sometimes, the 

 stoutness of these shoots, as given by their weight per unit of 

 length ; the weight of the total leaf-crop of the trees ; the weight 

 or size of the leaves, as determined by weighing or measuring 

 certain selected leaves, such as the sixth leaves from the ends of 

 about ten shoots ; or, lastly, the nitrogen assimilated in the leaves. 

 These various measurements were, of course, not always equally 

 applicable or convenient, nor could they always be expected to 

 give values even in the same direction : e.g. a certain form of 

 treatment might lead to the production of long, feeble shoots, the 

 total length of which would not be in proportion to the real vigour 

 of the tree : still less could they be expected all to give values 

 of the same magnitude; for instance, the percentage increase or 

 reduction in the size of the leaf would, as a rule,' be much less than 



