Problems of Physiological Plant Ecology. 4^ 



to measure the parts separately before it is possible to determine 

 the influence of the environment on plant activities. For con- 

 venience in handling these factors they have been classified into 

 climatic and edaphic, but I fail to see that such a classification 

 has any relation to the activities of the plant. It may, there- 

 fore, be suggested that these terms be dropped and that we 

 classify these factors according to their spatial relations into 

 those which are active above the soil surface and those which 

 are active below it. Each group must, of course, be further 

 analyzed according to the purposes of the investigation, but it 

 must be remembered that the data from separate component 

 factors usually needs to be again summed in order to express 

 the environment as a whole. For the great general problems 

 of plant geography it seems inadvisable to attempt too extended 

 an analysis, rather is it better to seek methods of measurement 

 which will furnish integrated measurements of groups of environ- 

 mental conditions. With our present lack of knowledge the 

 pressing of the analysis too far often results in such a complex 

 of data that interpretation is impossible. A fairly satisfactory 

 integration of the main air factors seems to be furnished by the 

 atmometer; as to the soil factors we have as yet practically 

 nothing in this direction. 



Temperature is very important in plant activities and we 

 have practically perfect instruments for its measurement and 

 for the construction of its curve. Unfortunately, we have as 

 yet no well-tested method by which temperature records can 

 be interpreted in regard to the effect of this factor on plant 

 behavior. A beginning which promises much has been made 

 bv MacDougal with his integration of the thermograph record, 

 and Professor Lloyd informs me that he has found a method 

 for interpreting maxima and minima. Here lies one of the 

 best fields for the scientific ecologist with a mathematical turn 

 of mind. 



Wind velocity can be measured and recorded by means of 

 the ordinary forms of anemometer, but the instruments are not 

 well suited to field work, largely on account of their expense. 

 Perhaps improvement may be forthcoming along this line. 



The conditions of humidity, which appear to be so import- 

 ant to plant life, can best be measured directly by means of the 

 dew-point apparatus, but the instrument is not as satisfactory 



