3. INFLUENCE OF PHYSICAL FACTORS ON TRANSPI- 

 RATION. 



Arthur William Sampson 



and 



Louise Marie Allen. 



Introduction. 



Transpiration, as a continuous and important physiological func- 

 tion of the plant, which is readily measurable, has long been an in- 

 teresting and important subject for investigation. As a rule, however, 

 investigators have confined themselves to the measurements of 

 transpiration independent of its relations to physical factors. Where 

 the latter have been considered at all it has been in a more or less 

 general way. The aim of the present paper has been to measure 

 transpiration along the following lines : 



1. To determine the individual variation of the same species 



grown and tested under the same conditions. 



(a) In the plant house; 



(b) In their natural habitats. 



2. To measure individuals of the same species, some of which 



had developed in the shade and some developed in the sun. 



3. To determine the effect of altitude and pressure on this func- 



tion. 



4. To determine the relation between the internal structure and 



the transpiration of an amphibious plant, and to compare 

 it with the internal structure and transpiration of land 

 plants. 



5. To test the effect of some of the common acids and alkalies 



on this function. 



6. To study the effect of three common soil types and the in- 



fluence of soil textures. 



It would seem that transpiration determined along these lines 

 should give results of value both from the theoretical and practical 

 side. For a study of sun and shade forms of the same species, 

 no plants could be more suitable than those developed in the vari- 



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