182 
Walter Stiles and Ingvar Jorgensen. 
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incomplete researches on isolated organs and imperfect generalis¬ 
ations derived therefrom, fails to realise the plant as a unit, or to 
consider it as a whole. Thus the law of the minimum and the 
special case of it called the principle of limiting factors are not of 
general application to the activity of the plant as a whole on account 
of the interaction of factors and the processes dependent on them. 
We are still waiting for the more exact statement which shall 
properly express the law of physiological relations—in other words, 
we are still waiting for a more satisfactory primary survey of the 
life of the plant. We are waiting, in fact, for that science of botany 
which will embody physiology, ecology and agriculture and make it 
the science of the living plant as a whole, having as its basis an 
elementary analysis of the plant’s activities in relation to environ¬ 
mental and hereditary factors. 
How little this broader outlook appears in the water culture 
method is apparent at once. We give a supposed definite 
composition of the nutrient solution and correlate this with the dry 
weight of the plant after an arbitrary time. There is no notice 
taken of alterations with time in the water culture solution; there 
is no notice taken of factors affecting the aerial part of the plant. 
No attempt is made at an analysis of how the plant is affected 
in its various phases, and there is a complete lack of conception of the 
possibility of broader investigations on dynamic principles. There 
is a complete lack of correlation between the various physiological 
processes : germination, assimilation, root absorption, transpiration, 
respiration, permeability, etc. There is generally an absence of any 
observations relating to hereditary factors. 
Under these circumstances it is no wonder that no simple 
principle has been brought out and no refined technique evolved in 
the case of water culture experiments, and that the whole method 
is more or less a matter of convention. Yet every piece qf work 
shows clearly the complexity of the matter, and indicates more and 
more the necessity for the realisation of it, and the impossibility of 
settling definitely questions of root absorption before a number of 
these elementary difficulties resulting from complexity have been 
removed. 
The Water Culture Method. 
We may now consider in detail some of the more obvious 
matters which call for discussion in the water culture method. 
1. Hereditary factors. In the majority of water culture experi¬ 
ments no account whatever is taken of the fact that differences may 
