178 The Plant World. 



ing. For the first 150 minutes the Mercurialis shoots lost 

 0.173 g. per hour, per 100 sq. cm. of area. For the first 90 

 minutes the corresponding rate for Siiacda was 0.350 g. The 

 last named plant exhibited the highest rate of water loss per 

 unit area, while Mercurialis showed the lowest. The author 

 determined the ''degree of succulence" of each plant as the 

 water content per 100 sq. cm.; for Mercurialis it was 0.95 g., 

 for Sahcornia 6.5 and 6.1 g., and for Stiacda 10.0 g. Thus t e 

 highest degree of succulence is accompanied by the highest 

 transpiration rate per unit area! Under a bell-jar with liumid- 

 ity about 56%, the relaiiie transpiration, (related to evapor- 

 ation from a water surface, =^) of cut shoots of Salicornii was 

 0.32 and of Vicia cracca, 0.26 for the first 2 ) minutes. This 

 means the unit area of Salicornii lost 32 '''r,<'>i Vicia 26 % 

 as much water as an equal area of free water surface 

 Here again the succulent loses moisture more readily, ^^r unit 

 of area exposed, than dees the mesplntc. Additional evidence 

 of a similar nature is presented b}- the author, who also points out 

 that, while other succulents (e. g. Sedum) thrive in rather dry 

 air, if plenty of water is applied to the roots. Sahcornia under 

 such conditions does not abs'^rb water through the roots as rap 

 idly as this is lost by transpiration. It thus appears that this 

 form of Salicornia (5. annua), at least, would not succeed unde 

 conditions of intense evaporation, even though its roots were in 

 salt-marsh water. But the air which usually bathes the stems 

 is of high humidity, and furthermore, as is shown in this article 

 the green surfaces absorb water rapidly when submerged, though 

 the absorptive process is not nearly so rapid as that of transpira- 

 tion in moist air, surface for surface. But little absorption 

 takes place from a nearly saturated atmosphere. 



Determinations were made of the number, size and dis- 

 tribution of stomata in several plants. It appears that, in 

 Salicornia and Aster tripolium these organs open and close with 

 light and darkness, while the plant is young, but that with the 

 coming of the flowering time this power of movement is lost and 

 the pores remain permanently closed. 



It is to be hoped that the author may continue this work 

 and determine the physical influence of stomatal movements 



♦Livingston, B E., The relation of desert plants, to soi moisture and to evaporatii/D . 

 Publication 50 of the Carnegie Institution 1906. 



