Variation as an Organic Function 165 
in the case of a colony of ants, the various galleries, chambers, food 
stores, etc., in the nest, and also the cultures of aphides, fungi, etc. 
which the ants control are all persistent secondary environmental 
factors, and therefore structural characters of the colony, regarded 
as a biological individual. It is possible, of course, to imagine a type 
of fluid organism exhibiting a very complex behaviour in relation 
to the outside world, but in which no obvious persistent environ¬ 
mental factors were recognisable. Fortunately for biological science, 
this is not so in most cases. 
One of the principal distinguishing characteristics of the organism 
regarded from any point of view is its individuality. From our 
standpoint, this is recognised by the fact that its activities are 
functionally integrated. By integration is not implied any physio¬ 
logical mechanism, but simply the observed fact that the organism 
behaves as a unity, as revealed by the existence of definite and 
constant types of correlation in various environmental changes. 
When for instance a plant is given a restricted water supply, it may 
check vegetative growth and hasten the process of flower and seed 
formation. This is a very complex phenomenon, involving the inter¬ 
action of several distinct trends of behaviour that permeate the 
whole organism. It can be explained most simply on the assumption 
that the various activities (i.e. the sequences of events which charac¬ 
terise the processes of growth and reproduction) are functionally 
integrated, and that the whole complex has the capacity of regulating 
the expenditure of the accumulated energy of the organism through 
various channels in different circumstances. 
Functional integration is moreover not confined to single organisms, 
but may also be an observed characteristic of the relation between 
different individuals. This is probably true, for instance, in certain 
cases of symbiosis, such as that between algae and fungi in lichens. 
Here also there is an observed co-ordinated behaviour in metabolism, 
growth, and asexual reproduction, in relation to a variety of external 
conditions. 
The integration of activity-systems, whether in the same or 
different individuals, is always associated with some kind of environ¬ 
mental-reaction 1 , but it is important to observe that the two phe¬ 
nomena are quite distinct. Two or more different organisms may 
interact physiologically, and even interpenetrate each other spatially, 
1 A generic term for any kind of energy-reaction associated with the life 
of the organism, including those which are internal or physiological, and those 
which are external or economic. 
