36 



LOUISE DOSDALL 



Comparing the transpiration of the different species of Equi- 

 setum, it is found that Equisetum hyemale loses but six-tenths 

 as much water as does Equisetum fluviotile and that Equisetum 

 arvense but four tenths as much, showing that these two are 

 more mesophytic species. 



{2) Guttation 



Leaves of many species of plants, among which the best 

 known are aroids, fuchsia, cabbage, and nasturtium, exude drops 

 of water from their surface when transpiration is checked by 



h 



Fig. 3. A. Stem of Equisetum hyemale showing drops of water exuded by 

 guttation. B. Equisetum arvense showing drops of water exuded by guttation. 



-external factors. (Sachs 1887: 278). Usually the water is forced 

 out of permanently open stomata or water pores at the end of 

 the veins. Although a common phenomenon, it is scarcely to 

 be expected in a xerophyte. During the week of May 18-23 

 on four successive cloudy mornings, all three species of Equise- 

 tum were found to be guttating vigorously. In some cases the 

 drops of water were 4 mm. in diameter, and 25 to 50 occurred 

 on single stems. Old stems as well as young were exuding water 

 (fig. 3). On these mornings the relative humidity in the 

 greenhouse was 72%. The plants were then placed under bell 



