204 The Living Plant 



which, called a Transpirograph (a little thing of my own, by the 

 way) is shown in operation in the accompanying photograph 

 (figure 69). By its use the plant is made to write, precisely and 

 continuously for days together, a record of its own transpiration. 

 Further, there also exist instruments, invented long ago for use 

 in meteorological stations, which write continuous records of 

 the very conditions that affect transpiration, viz., tempera- 

 ture and humidity, while light is recorded by a special method. 

 When the cotemporaneous graphs of transpiration and the 

 external conditions are plotted together upon the same sheet, as 

 in case of the accompanying graph (figure 70), the relation be- 

 tween process and influencing factors is displayed in a way 

 which leaves little to be desired in the direction of exact and ex- 

 pressive exhibition of the relation between this physiological 

 process and the external conditions. Indeed, I am accustomed 

 to use this study with my own students as an example of a well- 

 nigh ideal piece of physiological method, whereby Nature is 

 compelled not only to display, but, even to write down, for the 

 edification of man, the tale of her own operations. I often recall 

 with delight the remark once made by an eminent literateur who 

 happened to visit my laboratory at a time when this experiment 

 was in progress. As soon as he had grasped the full scope of the 

 matter, he turned away with this comment, "Well, I don't see 

 what there is left for Nature to do but lay down and holler." In 

 these words he expressed very well both the aim and the joy of 

 scientific investigation, which after all is a kind of great game 

 where one matches wits against Nature, and generally loses, but 

 now and then wins and gathers the stakes, which consist in a 

 share of her jealously-kept secrets. 



But to return to our experiments on the effects of external 

 conditions upon transpiration, they show these results. Heat 

 increases, and cold lessens it. Heat, indeed, may hasten tran- 

 spiration to such a degree that water is lost from the leaves much 

 faster than the roots can absorb it or the stems conduct it, in 



