Sampson and Allen : physical factors on transpiration. 47 



From the foregoing tables it is evident that sun forms transpire 

 more than shade forms. This not only holds when the plants are 

 measured in their natural habitats, but also when both forms are 

 subjected to either sun or shade. With both forms in their natural 

 habitats, the sun form loses from one and one-half to four times as 

 much as the shade form. With both forms in the sun, the sun form 

 loses from one and one-half to three times as much as the shade 

 form. When both forms are subjected to shade, the transpiration in 

 Ihe sun form is from one and three-tenths to three times that of 

 the shade form. 



These results are quite at variance with what would be the a 

 priori opinion of botanists in general.^ However, the greater trans- 

 piration of the sun form is accounted for, in part at least, by the 

 greater number of stomata per unit of leaf surface as compared with 

 the shade form. Further, the greater amount of chlorophyll in the 

 tissues and the consequent greater activity partially explains the 

 greater transpiration of the sun form. 



A still further investigation on the effect of transpiration in vari- 

 ous habitats was conducted at the Alpine Laboratory. Four sta- 

 tions were selected on the merits of their contrast in physical fac- 

 tors. Four dififerent species with five plants of each were measured 

 in potometers in these habitats and two checks made in each case. 

 The following tables show the measurements of the physical factors 

 in the respective habitats and an average of all transpiration results 

 obtained. 



TABLE VII. 

 Physical Factors. 



Formation of habitat Light Water-Content Humidity Temperature 



Satura- Normal Available Air Surface Soil 



tion point 



Station I — 



Brook Bank 02^0 .51% 35'40% 25-30% 727o 58° 55° 50° 



Station II — 

 Gravel Slide 6 15 5-6 2.5-5.5 48 62 100 68 



Station III— 

 Spruce Forest ...... .03 45 18-22 12-16 55 60 62 51 



Station IV— 

 Half Gravel 6 20 ^6-9 4-5-7-S 43 63.5 62, 58 



^ Weisner, Biologie der Pflanzen, 1902, p. 11. 



