34 MINNESOTA BOTANICAL STl^DIES. 



ous habitats found in the vicinity of the Alpine Laboratory at Min- 

 nehaha, Colorado, where the light, temperature, humidity, and soil 

 moisture content are extremely variable in the different habitats. 



The major part of the investigation was carried on in the Depart- 

 ment of Botany of the University of Nebraska, and at the Alpine 

 Laboratory at Minnehaha, under Dr. F. E. Clements. The minor in- 

 vestigation of the effect of soils was done independently by Arthur 

 W. Sampson, in the Department of Agronomy, Division of Soils, 

 under Prof. Alvin Keyser. The physical factors cited in the various 

 formations at the Alpine Laboratory are those determined by Dr. 

 Edith Clements. ^ Grateful acknowledgment is made for their use. 

 Helpful suggestions were made froai time to time by Dr. C. E. Bes- 

 sey and Dr. F. D. Heald, and appreciation is here tendered for the 

 facilities offered by the Department of Botany at the L'niversity of 

 Nebraska, and at the Alpine Laboratory, Minnehaha. Colorado. 



Working Plan. 



No mode of determining the loss by transpiration is free from 

 error. The method ■ of measurement resorted to with all 

 alpine forms was by weighing leafy twigs with the cut ends im- 

 mersed in water. Several vials were used with tightly fitting corks 

 having a perforation in the centre through which the stem was in- 

 serted. The corks were tightly sunk below the mouth of the vial, 

 and the depression filled with a mixture of vaseline and plaster 

 paris, about the consistency of gum. Over the top of the vial and 

 fitting closely around the stem was stretched a piece of rubber tis- 

 .sue. 



Weighing the leafy stems with the cut ends immersed in water 

 in this way, is not likely to afford the same absolute amounts of 

 loss by transpiration as would be given by the same twigs supplied 

 with water by the normal root pressure of the plant. But the leaves 

 are in a normal atmosphere, and their relative losses .(as compared 

 with each other) may be very nearly the same as under absolute- 

 ly natural conditions. Besides, the use of the potometer is indis- 

 pensable where one wishes to determine the loss by transpiration 

 of trees or shrubs where only a part of the plant can be used. In 

 no case were weighings made after the leafy stems had been in 

 potometers more than four days, or after the leaves showed the 

 slightest signs of wilting or drying. 



In the plant house the pot method was used entirely, the soil 



' Relation of Leaf Structures to Physical Facts, 1905. 



