vii OSMOTIC PRESSURES OF LEAF CELLS 149 



vessel into which the branch dipped was found to have 

 gained 0'400 gr. During this time the old leaves had 

 become flaccid, while the young leaves remained turgid. 

 Even the old leaves did not become markedly flaccid during 

 the first forty minutes of the experiment. 



(3) A branch with 8 leaves was exposed to a pressure 

 of 6 atmospheres during one hour mostly of bright sun- 

 shine. During this time the leaves showed no signs of 

 becoming flaccid, but the surface lost some of its gloss. 

 On weighing, it was found that the vessel below had lost 

 0*007 gr. of water. This amount, however, comes within 

 the limits of error of the experiment, and, consequently, 

 we may assume that neither upward nor downward motion 

 of water occurs in these branches when the leaves are 

 exposed to a pressure of 6 atmospheres. In this experi- 

 ment, when the pressure was removed, the leaves recovered 

 their gloss. 



(4) Against 4 atmospheres, the same branch, in inter- 

 mittent sunshine, transpired 0*622 gr. in one hour and 

 twenty minutes, while all the leaves remained quite turgid. 



At the conclusion of the series on this branch the amount 

 it transpired at normal pressures still surrounded with 

 carbon dioxide gas was measured, and was found to be 

 1 *244 gr. in one hour and ten minutes. In air at normal 

 pressure the same branch transpired in one hour 0*966 gr. 

 During these last two experiments, the leaves were slightly 

 faded. 



The decrease in the rate of transpiration with the in- 

 crease of pressure which is indicated by these results is, 

 doubtless, more marked than here appears, as it is well 

 known that the rate of transpiration of a branch falls off 

 rapidly from the time of cutting it. In Experiment 3, 

 at 6 atmospheres, which was the second to be made with 

 this branch, this decrease would have been small, but in 

 the succeeding experiments would have become more 

 exaggerated. 



