ECOLOGICAL SUCCESSION. 93 



isolated facts into a science on the basis of mores, including habitat 

 preferences. The similarities between the response phenomena 

 of plants and animals have led in the direction of the organization 

 of a branch of biological science embracing both plants and 

 animals. It is this organization, or the possibility of organiza- 

 tion, which we are attempting to introduce here. The experi- 

 mental work cited above is adequate to indicate the lines along 

 which further investigation should be directed and that the 

 mores problem, which includes the habitat preference problem, is the 

 central problem of ecology. 



VII. SUMMARY. 



1. The development of forest on sand or other mineral soil is 

 accompanied by an almost complete change of animal species and 

 piobably by a complete change of animal mores (pp. 67-72). 



2. Forest development is accompanied by marked changes in 

 soil and physical factors; animal distribution is more closely 

 correlated with differences in physical factors than with species 

 of plants (pp. 73-82). 



3. For animals living in the soil, the moisture equivalent, or 

 the wilting coefficient for a standard plant, is the best index of 

 the moisture available to the animals (p. 74). 



4. The rate of evaporation or the evaporating power of the air 

 is probably the best index of the conditions of the atmosphere 



(p. 77). 



5. The rate of evaporation, temperature, etc., have been found 



to be very different in the different communities and also different 

 in the different strata of the same communities. The amount of 

 evaporation in animal communities is directly related to their 

 order of occurrence in succession (p. 81). 



6. Plant and animal communities are divisible into strata 

 which represent vertical differences in physical conditions. The 

 bodies of many plants occupy several strata but their vegetative 

 parts are usually in some particular stratum. Land animals are 

 comparable to smaller "non-rooted plants such as algse, lichens 

 and fungi. Many animals carry on different activities in dif- 

 ferent strata, but are to be classed primarily with the stratum in 

 which they breed (p. 84). 



