THE PLANT WORI.D 133 



celluloid will keep the pieces appressed to each other. After a prelim- 

 inary drying of the cobalt paper, this device may be adjusted by engaging 

 a portion of a leaf blade between the folds of the cobalt paper, which will 

 be pressed firmly but not too tightly to the upper and lower leaf surfaces of 

 the celluloid. The relative rapidity of the transpiration of the upper and 

 lower surfaces may thus be determined in the same leaf at the same time. 

 Any number of these little appliances may easily be made at a trifling cost. 

 An important pedagogical advantage lies in the ease with which accurate 

 comparative results may be obtained by 3-oung pupils. Those of our 

 readers who wish to test this device may each receive one upon applica- 

 tion to the editor of this department. 



The cobalt method is of course qualitative only, although this does 

 not decrease its value when used for obtaining comparative results. If 

 it is desired to know the exact volume of water given off by a plant, 

 other methods must be used, of which the one most commonly used in 

 elementary work is that of weighing a growing plant. Every one is 

 more or less familiar with this method through its exposition in the 

 various text-books. It is worth while however to point out here that 

 the results of this experiment may be made much more vivid to the 

 student if the loss of weight is represented by a corresponding volume 

 of water. Thus, when a small geranium with five leaves was shown to 

 lose 5.5 grams of water in twenty hours — 5.5 cc. of water were then 

 measured out in a graduated vessel. To what the loss of weight is due 

 must be shown by a qualitative experiment, for which, as suggested 

 above, cobalt paper may be used. 



FIELD STUDY OF POLLINATION. 



Much as has been done upon this part of botanical study, the subject 

 is still open to investigation with a promise of useful results, if a fair 

 amount of time and patience, coupled with careful observation, be put 

 upon it. This is evident, to speak specifically, from the results of recent 

 observations made on the English Primrose, one of the plants which 

 Charles Darwin studied, by two English naturalists. We shall take occa- 

 sion, in a subsequent issue, to summarize these studies. Meanwhile, we 

 would point out that we have in this country many plants similar to the 

 primrose, in that they have heterostyled flowers — i. e., the style is long in 

 the flowers of one and short in tho.se of another individual. Our common 

 Bluet is one of these. We would like very much to get the cooperation 

 of a number of observers in collecting data concerning this plant. What 

 can be done is indicated in this brief outline : 



Select a definite area well occupied by plants, and direct attention to 

 these as continuously and often as circumstances will permit. Make a 

 rough estimate of the number of flowers open ; note weather condition at 



