148 BOTANICAL GAZETTE [FEBRUARY 
record for a week. The tripod stand is adjustable for height, and can be 
leveled, while the mechanism in use is protected by a glass bell-jar. 
Such is the instrument in its present form.3 For some special purposes, 
such as for use out of doors, it would be better to have the weight-cylinder 
and the recording drum separated, so that the latter may be removed to 
any desired place in laboratory, lecture-room, or elsewhere. Probably 
this form. will later be obtainable. For greenhouse and general demonstra- 
tion use, however, the arrangement figured will be found most convenient. 
The releaser and reservoir are arranged for gram weights, which are the 
only ones likely to be needed in educational work. For special investi- 
gation purposes lighter or heavier balls could of course be used after appro- 
priate alterations in the size of reservoir and releaser. The instrument 
may be used with any balance sensitive to a gram; but a special balance, 
adapted expressly for transpiration work, and provided with a mechanism 
to prevent oscillation under action of the wind, is in preparation, and will 
later be described. 
IV. ADJUSTABLE LEAF-CLASP. 
In several phases of the study of the physiology of leaves it is necessary 
to apply some object or special device to two exactly corresponding areas 
of the two surfaces of a leaf. The most familiar instance of this occurs in 
the application of Stahl’s cobalt chloride method to the study of transpira- 
tion, and there are other cases nearly as important. For these purposes 
some simple devices are improvised from clamps, watch-crystals, mica, 
etc., but there is at present no obtainable appliance by which this end can 
be accomplished with certainty, celerity, and convenience. The new 
leaf-clasp, designed to meet this need, is illustrated in the accompanying 
fig. 3, and is constructed as follows. Two similar brass rings, ‘‘chambet- 
rings,” each 3o™™ in diameter and 5™™ in depth, are attached at the 
ends of parallel flexible-elastic bars, so arranged that they hold the rings 
firmly and exactly edge to edge, while allowing of their separation, by 
means of a screw, to any desired extent.4 For each ring there are provided 
two accessory rings. One of these is right-angled in section and holds 4 
removable cover-glass, so that when pushed over the exposed edge of the 
chamber-ring, it converts the latter into a glass-topped chamber, as show? 
in the figure. If disks of filter paper treated with cobalt chloride (and 
3 While this description is in press it has been decided, in order to give the inst™ 
ment greater compactness, to place the weight-cylinder and recording drum side by 
side, instead of one above the other. 
4 In the final form of the instrument, a second screw, not shown in the figure, 
has been added, permitting the rings to be brought still more tightly together if needful. 
