266 BOTANICAL GAZETTE [ APRIL 
the same box and follow development of the same seedlings for 
several weeks. 
7. A transpiration device. 
In preparing plants for transpiration weighings it is usual to 
wrap the pot in rubber cloth. This prevents the condition of the 
pot with respect to water being seen, and limits the supply of 
oxygen to the roots. If, instead, the pot be placed in a thin 
glass dish slightly larger in diameter than the pot, and one to 
two inches higher, it will be necessary only to roof it over with 
rubber, which is much easier than wrapping the whole plant ; 
the condition of the soil may be seen and more or less water 
given as seems needed; and the oxygen supply for the roots is 
more nearly normal. Of course plant and glass are weighed 
together. 
8. The graduation of roots, tubes, etc. 
In experiments on growth and geotropism, one often needs 
to graduate rocts, which is done with insoluble India ink. But 
when the ink is applied with a pen or brush, it generally runs and 
is very uneven in breadth of the lines. If a fine thread, = 
stretched by the spring of a piece of wire, be used, and the 10 
placed on and allowed to soak into it, marks of perfect oom 
ness and any desired breadth may be made by the thread. ts 
of course equally good for glass tubes. The thread and = 
may be mounted conveniently in a needle-holder. A ex 
frame could be made with threads 1™™ apart and parallel, w 
which a root could be graduated perfectly in one operation. 
9. A root-pressuze gage. 
Root pressure is so important a subject that an oe) 
for its measurement is much needed. None, bor er 
able; the apparently simple $-shaped tube conta = eat 
figured in most books, cannot be made to work i 
difficulty. Figure 7 shows a form which, while peer ults. A 
errors, yields, nevertheless, approximately correct ae at 
tube six inches or less long, with a good glass wer gor divi- 
top, is graduated, as just described, into convenient . 
sions, and is then attached to a stump of 2 V8 
ent gage 
is avail- 
cury, 
orous P 
