266 BOTANICAL GAZETTE [october 



shade rose until 3 P. m,, it is possible enough that its bleeding 

 was coincident with its hours of becoming warmer. That the 

 sap became bitter and astringent shows that its extrusion was not 

 due to any normal activity of living cells ; but the true explana- 

 tion is probably the same as that of Pitra's experiments. Pitra 

 made numerous experiments differing from Baranetzky's in that 

 the piece of a stem was submerged except the upper end, which 

 was provided with a manometer. Bleeding was likely to begin 

 after eight or more days. Pitra had here substantially the same 

 physical apparatus as an osmometer. The sap in the wood is 

 slightly more concentrated than the water outside ; between 

 them the cambium or youngest immature wood would be a very 

 imperfect semipermeable membrane, and the callus or healing 

 tissue formed in and over the exposed surface within a few days 

 (cf. Molisch, 1902; Wieler, 1893: 150) would make a much 

 better one, A continuous layer of uninjured cells between the 

 sap and the water would insure success ; accordingly when the 

 leafy branch was immersed and the cut end, with the manometer 

 attached, was above the water, a pressure was more' certain to 

 be developed. This experiment shows also that in such experi- 

 ments the water moves toward the base of the stem just as well 

 as toward the leaves, Wieler (1893: 30-33) has repeated these 

 experiments, likewise making an osmometer each time, so that | 



his results are most naturally construed as having no bearing on 

 the normal movement of the transpiration stream. C. Kraus has 

 published an enormous number of instances of so-called bleed- \ 



ing from various isolated parts of plants In at least a part of 

 these the conditions were such that by the formation of a wound 

 tissue an osmometer was formed. I have not had access to all 

 of C. Kraus' work, but what I have seen makes me quite ready 

 to accept the opinion of Molisch that the extrusion of water was 

 always a direct or indirect effect of wounding, and without any 

 relation to the rise of sap in healthy plants. Molisch's own 

 work (1899) on the voluminous bleeding of sugar producing 

 palms was more of a puzzle in the absence of information on the 

 histogenetic results of the wounds inflicted, until his paper of j 





