AGRICULTURAL EXPERIMENTS 255 



particular fungus late in the year, and though they are equally 

 exposed to the possibility of infection the neighbouring plots 

 remain perfectly healthy. We can only conclude that differences 

 in the nutrition of the plants have produced such differences in 

 the composition of the leaf cells that the fungus can find a 

 medium for its development in one case and not in the other. 

 But as indicated above these differences of composition which 

 lead to such widespread results are extremely elusive and 

 difficult of investigation. Just the same thing is true for the 

 science of feeding animals. In the early days certain fundamen- 

 tal questions of this character were dealt with at Rothamsted. 

 The composition of the carcases of sheep, oxen and pigs at 

 various stages of fatness was established, as were the relations 

 of food to increase and the origin of fat in the animal's frame. 

 But the science of nutrition has now passed out of that early 

 region of first approximations : we know that carbohydrates 

 and fats supply energy which can be stored in known ratios ; 

 we know, roughly, what quantities of protein are required to 

 maintain the tissue wastage. What is now required is an attack 

 upon a much more refined class of problem — why an animal in 

 the last stages of fattening responds so well to linseed cake and 

 acquires a special kindly feel and appearance on this food alone ; 

 why again cotton cake and barley meal " nick " so well together; 

 why again oats must not be fed to horses until they have been 

 in store for a certain length of time. These are all questions 

 which depend upon much more delicate methods of analysis 

 than those hitherto available, because they deal with constituents 

 untouched in the first approximation to the composition of the 

 material present perhaps only in minute proportions. 



The influence of climate and season has naturally received 

 much attention at Rothamsted but it cannot be said that 

 any great advances have yet been made in the way of corre- 

 lating meteorological statistics with growth. Temperature and 

 water supply are without doubt fundamental factors in deter- 

 mining yield ; the difficulty that attends the problem seems to 

 be the collection of data that are really critical. For instance, 

 everybody will agree as to what constitutes a spell of "growing 

 weather " in spring but it is difficult — we may almost say it is 

 impossible — to define such growing weather in terms of the 

 constants usually determined at a meteorological station or to 

 pick out from an inspection of the daily readings when such 



