134 
Sv UN I'.V H. VlTJES. 
Yellow light acted upon them in the same way as darkness, thc rays 
which were active in ehecking over-growlh and in causing histological 
difT'erentiation belonging to the more highly refrangible porlion of the 
Spectrum. 
At the time when Brefeld’s paper was published. I was engaged in 
the following observations upon the growth of Phycomyces nitens, one of 
the larger Moulds. This plant is very sensitive to the action of light, 
for it exhibits a well marked positive heliotropism, but it is not so sen¬ 
sitive as the Pilobolus with which Brefeld experiinented, for exposure to 
darkness or to yellow light during the whole period of its growth did 
not produce any appearance of etiolation. All that can be said in this 
respect, is that the hyphae were rather longer, when they had grown in 
the dark than when they had grown in the light, and that they grew 
longer in yellow light than in blue, but the differences were coropara- 
tively slight. The object of the experiments was to obtain evidence of 
the action of light in retarding growth in a very simple örganism, and 
from the knowledge thus acquired to seek an explanation of the phe- 
nonteua. 
The melhod pursued in obtaining the material for observalion was 
that suggested by Brefeld 1 ). Spores of Phycomyces were diffused through 
the w'ater contained in a watch-glass by placing in it a malure sporan- 
gium which immediately burst. A few drops of this water were then 
transferred by means of a needle to a piece of bread soaked with solution 
of grape-sugar. Under these circumstances the spores rapidly germinated 
and gave rise to a vigorous growth of the fungus. Upon this first crop 
a thick glass plate, with two or three holes in it, was laid. so as to arrest 
the further grow th of the existing sporangiferous hyphae. In a few hours 
new hyphae had grown through the holes in the glass plate. In this way 
it was possible to obtain the hyphae sufficienlly isolatcd to admit of ob¬ 
servalion , and their small number caused their growth to be more than 
usually vigorous. 
The apparatus for the measurement of growth was suggested by 
Professor Sachs, and is shewn in Fig. I. It consists of a stand I) sup- 
porting a clockwork C, of which p is the pendulum. Connected w r ith the 
clockwork by a cog-wheel is a shal't ff, bearing a plate t, on which the 
object to be observed Stands. The piece of bread, on which the Mould 
was growing, was placed in a small glass dish moistened with water, 
and covered with a bell-jar B, so that the moisture of the air surroun- 
ding the Mould might Vary as little as possible. Through the cork which 
closed the neck of the bell-jar, a thermometer passed into the inlerior, 
I) Meth. z. Untersuch, d. Pilze. Verhnndl. d. phys. med. Gesellsch. in Würz¬ 
burg. N. F. Bd. VIII. 1874. 
