VI. The Inltuenco of Light upon Ihe Growth of unieellular Organs. 
135 
liy means of which varialions of lemperalure in the ncighhourhood of 
the plant couid be ascertained. On the stand stood also thc micro-tele- 
scope A. lhis inslrument eonsisls of a heavy iron foot f , inlo which the 
shaft d, which bears the lube, fits. The shaft d ean be moved upwards 
or downward and can be fixed in any posiliou by means of a screw. 
This is the coorse adjustment 
of the inslrument. The tube 
is fixed in a holder, which 
forms part of the eap b. This 
cap fits on lo the upper end 
of the shaft d, and can be 
raised or lowered b\ means 
ol the screw a. This is the 
fine adjustment of the instru- 
ment. On tlie upper surface 
of the cap is a gradualed 
disc, and it is possible to 
ascertain the number of de- 
grees through which the 
screw has been turned, by 
means of a poiuter attached 
to it. The tube itself is a 
micro-telescope devised espe- 
cially for observalions of this 
kind by Professor Qijixcke, 
and conslrucled by Steinbeil 
of Munich. The eye -piece 
contains a micrometer, by 
means of which the measu- 
rements are made. When 
■ the inslrument was focussed 
upon a growing hypha, and 
the uppermost line of the 
micrometer seale was brought, 
by means of the (ine adjust- 
mcnt, to maik the position of the apex of the hypha, it was easy to read 
° t ie number of divisions of the scalc through which the hypha had 
grown in any given time. 
The oljject of the clockwork is lo cause the object under observalion 
..° l0la,e so as to av °id heliolropic curvatures when it is exposed to 
'gib In order that the condilions under which the observalions were 
mai e nlight be as far as possible constant throughout, the rolalion was 
11 II1UU wllen lhe P lant w as in darkness. ln order to shut off Ihe 
