478 Forestry Quarterly 



when the leaves of a branch are killed, not only is the flow of water 

 greatly reduced, but finally the leaves dry up and ultimately fail 

 entirely to raise water in the branch. It is true that in this case 

 not only are the vital actions removed, but also one of the most 

 important features of the mechanism, that is, the semi-permeable 

 membrane is destroyed by coagulation of the protoplasm. It is 

 evident, however, that after the death the capillary forces of the 

 cell wall of the leaf cells alone are unable to raise the water under 

 the new conditions, and this would suggest that unaided they may 

 be insufficient in the living leaf. This line of reasoning would 

 indicate that the protoplasm may not only act as a semi-permeable 

 membrane by allowing water to pass through to a region of 

 diminished presstu*e, but it may also actively secrete water on its 

 outer surface. We know that such glandular action of protoplasm 

 takes place on the exterior of the filaments of certain fungi, and on 

 the leaf margins of certain higher plants. The author collected 

 the drops exuded on the margins of a leaf and fotmd that they were 

 practically pure water, their density being less than that of tap 

 water. The author concluded that osmotically the exudation 

 may be regarded as pure water, and consequently the process 

 must be one of secretion involving the intervention of living 

 protoplasm and the expenditure of stored energy. 



Now, the question arises as to how far the glandular function 

 of certain leaf margins can be transferred to the mesophyll cells 

 bordering the stomatal chambers of transpiring leaves. The 

 author performed several experiments bearing upon this point. 

 In one of these he fixed a leafy branch water-tight into the low 

 opening of a glass receiver, so that its upper part and leaves 

 projected into the interior, while its base extended into an aqueous 

 solution of eosin. The receiver was then filled with water, so 

 that the branch was completely submerged. The proper pre- 

 cautions were taken before the experiment began to equalize the 

 gas pressure in the branch with that of the atmosphere. Although 

 the leaves were covered with water, and although they were sub- 

 jected to hydrostatic pressure due to the depth of water, sufficient 

 in some cases to drive the liquid back into the intercellular spaces 

 of the leaves, the eosin mounted rapidly into the branch. The 

 eosin rose most rapidly when the apparatus was in strong light and 

 when bubbles of oxygen were being given off at the siirface of the 

 leaves. When the apparatus was placed in the dark, there was 



