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git] OVERTON—TRANSPIRATION AND SAP-FLOW 43 
several years of experience with classroom experiments, it has 
been found that the common umbrella plant, Cyperus alternifolius, 
is a very suitable species for such experimentation. The plants 
are easily cultivated in the greenhouse, often reaching 60-90 cm. 
- or more in height. The aerial stems are free from nodes and leaves 
except at the top, where the large, many-rayed involucre of narrow 
leaves is situated. The younger leaves are comparatively trans- 
lucent, permitting easy observation of the rise of colored liquids 
such as eosin solutions. As will be seen below, the plants transpire 
rather rapidly as compared with those in ordinary use for laboratory 
experiments, giving off fairly large quantities of water per unit 
area of leaf surface. The rate of sap-flow is of course correspond- 
ingly rapid. Further, the stems and leaves are not easily injured 
y the mechanical manipulation often necessary in such experi- 
ments. Cyperus papyrus is also an excellent plant for comparative 
study.on account of its longer stems, but the fading of the leaves 
is less readily observed, owing to their narrow threadlike form. 
The character of the involucral leaves allows a glass tube or 
LieBiG condenser of suitable diameter and length to be readily 
slipped over the crown and down on the stem without injury to 
any part of the plant. Two-holed rubber corks may be split and 
clamped about the stem above and below and fitted into the glass 
tube. If small glass tubes are bent at right angles and inserted 
into the remaining holes of the corks, an inlet and outlet for steam 
is easily arranged. The steam may be conducted away to any 
distance so as not to injure the plants except in the desired region. 
The method of arranging the experiment is shown in fig. 1 By . 
clamping the rubber connections and leaving the incasing glass 
tube on the plant after treatment, the stem is inclosed in a sterile 
chamber and is kept in a moist atmosphere which prevents its 
drying and does away with the necessity of using paraffin or 
other protective covering. If it be desired to use melted paraffin 
or wax, this may be poured into the tube, thus inclosing the 
injured region. In using a poison instead of steam, the fluid may 
_ be poured into the tube at the top and drawn off at the bottom 
after the treatment is finished. I have successfully used grafting 
Wax to further secure the corks and connections and prevent 
