1913] LIVINGSTON—TEMPERATURE COEFFICIENTS 351 
Furthermore, the internal conditions (or the nature) of an 
organism being duly considered, the success attained by it in any 
locality is an index of the extent to which the environmental 
conditions of that place have been favorable to successful growth, 
both vegetative and reproductive. Thus it frequently becomes 
apparent that the conditions of one locality have been more or less 
favorable to the success of a given form than have those of another 
locality. 
The difficulty, however, which ecological science has not yet 
been able to surmount lies in the extreme complexity of the system 
of conditions which affect the success of organisms. The numerous 
component factors of an environmental complex fall into categories 
of water, non-aqueous materials, heat, light, and mechanical conditions. 
It is obvious that the limiting condition that has prevented the 
occurrence of a certain plant, for example, in a given area, may 
belong to any one of the foregoing categories; mechanical conditions 
may have failed to bring the seed hither, moisture conditions, or 
other conditions of material supply or removal, may have anni- 
hilated the plant after it was really introduced, or annihilation may 
have followed from adverse temperature or light conditions, etc. 
The distributional problem is made still more complicated and 
difficult by the perfectly clear but seldom emphasized proposition, 
that each separate or component condition of an environmental 
complex is a variable in at least two dimensions, as it were; each 
such condition must always be considered with regard to its intensity 
and also with regard to its duration. To illustrate by means of a 
water factor, a desiccated soil may cause the death of a given seed, 
but this result would probably not be accomplished if the soil were 
dry for only a day or a month; the condition of dry substratum 
must be maintained for a certain minimum period if it is to be 
effective as a limiting condition. Some less well defined environ- 
mental factors have to be considered in regard to a third dimension 
which may vary, namely, quality. Light, for example, may reach 
chlorophyll tissue in seemingly sufficient intensity and during an 
apparently sufficient time period to produce a requisite amount of 
carbohydrate, but this may fail to happen because the radiant 
energy is of too short or too long wave-length. Here quality is as 
important as is either intensity or duration. 
