1915] BRIEFER ARTICLES 23% 
dish could be rotated and the radicle of the seedling quickly brought to 
any desired angle with the vertical. 
The makeshift apparatus served the purpose fairly well, but the 
tumbler support was not always convenient. A special support was 
then constructed. As will be seen from the drawings, the support con- 
sists of a circular trough (of brass) mounted on a pedestal. There are 
two sockets for attaching the trough to the pedestal, which screws into 
the socket. These sockets are 90° apart. -The purpose of the extra 
socket is shown in fig. 2, where the tropism chamber is shown attached 
to a regular laboratory support. This arrangement is for use with the 
horizontal microscope.t The 
chamber may be transferred 
from the base to the laboratory 
support without altering the posi- 
tion of the seedling. 
ig. «t shows the chamber 
provided with a strip of cork so 
as to make room for several seed- 
lings. The drawing is from an 
experiment to illustrate trau- 
matropism. 
Fig. 3 shows the improved 
apparatus. The support is 
provided with a scale marked in 
degrees. This makes it possible 
Four marks etched or scratched 
on the cover of the Petri dish Fic. 2 
go° apart serve as pointers. 
Into a hole, bored through the bottom of the Petri dish, a cork is inserted. 
The seedling is pinned to the inner face of the cork. The cork can be 
_ moved from the outside and it is possible, therefore, to make the final 
adjustments of the position of the seedling (for example, bringing the 
radicle parallel with the faces of the chamber) without opening the 
Petri dish. 
* The tube from any compound microscope, clamped to a laboratory support, 
will serve as a horizontal microscope. A hair stuck to the diaphram in the eyepiece 
will serve as a cross-hair. 
