Tg11] OVERTON—TRANSPIRATION AND SAP-FLOW III 
to the action of poisonous or plasmolyzing substances in them, 
which interferes with the osmotic action of the cells and thus 
inhibits their lifting power. Ursprune regards this suggestion 
as an empty conjecture. 
My results agree well with those of RosHarpr, except that in 
the plants treated with steam I have never observed an increase 
in the amount of water given off during any one period over that 
in the preceding, such as is shown by RosHarpt’s table. It 
appears to me that if the living cells of the stem are necessary to 
the ascent of water, as RosHARDT contends, there could not pos- 
sibly be an increased amount of water transpired during any one 
interval over that of the preceding. The general gradual falling 
off in the amount of water transpired after killing a portion of 
the stem, which RosHarpr records, agrees with my observations 
on Cyperus under similar circumstances, except that the diminu- 
tion in the amount of water lost, after steaming a section of the 
stem, is continuous. I feel that the cause is the same in both cases, 
namely, a stoppage of the vessels, which I have actually shown to 
occur in Cyperus, and a probable injury to the leaves due to dele- 
terious substances being introduced into them. It seems to me 
that RosHarpt has placed exactly the opposite interpretation 
on the results of his quantitative experiments to that which they 
really show. 
Microscopical examinations of the stems of Cyperus above a 
steamed stretch show that some of the vessels are plugged for a 
considerable distance with a brown, gumlike gelatinous mass, 
which reacts to alkanin like resin. This substance is insoluble in 
water and often stops the vessels throughout the length of the 
stem above the killed portion, even plugging some of the tracheae 
of the leaves. There can be no doubt that this stoppage of the 
vessels in Cyperus accounts in a large measure for the immediate 
and constantly diminished water supply which reaches the leaves 
above a steamed portion of the stem. The discoloration of the 
contents of the sieve tubes is conspicuous, and suggests that the 
steaming causes considerable disorganization, which may be the 
source of the resinous substances in the vessels. Although 
Ursprune observed stoppage in several plants, he thinks that the 
