566 Ward. — Culture of Algae. 
It may also be added that I have been able to observe the 
division into zoospores of certain Protococcoideae in hanging 
drops of agar, and that this appears to occur only during 
the night. 
In connexion with the action of light on green Algae, ex- 
periments in which ordinary (reflected) light was allowed to 
act on agar plates of Protococcoideae, covered with a stencil 
letter, showed its effect in a few days ; the Algae in the area 
exposed to light developed normally, but those in the non- 
illuminated parts remained undeveloped. Consequently a 
faint green letter appeared in a colourless ground. 
When the light was more intense, however, the exposed 
Algae were killed, whereas those in the covered parts of the 
agar developed fairly well, and thus the surprising pheno- 
menon of a colourless letter in a green matrix appeared. The 
development in the shaded parts was probably due to the 
reflection of some of the intense light at the back of the plate, 
and this diffused over the non-exposed area was strong 
enough to enable the Algae to grow, but not sufficiently 
intense to kill them. 
Many questions involving the use of quartz and coloured 
screens, and of different sources and intensities of light 
arise out of these experiments, and are held over for further 
investigation. 
EXPLANATION OF PLATE XXVIII. 
Illustrating Prof. Ward’s paper on the Culture of Algae. 
The upper curve represents the growth of the filament referred to on p. 565, 
and the lower curve the changes of temperature. 
The curves start at 3.10 p.m. on Aug. 27, when, as seen from the table (p. 565), 
the filament measured 58*5 \x in length. The shaded areas represent the hours of 
darkness of each successive night. 
It will be seen that the period of maximum growth coincides with that during 
which assimilation is active — i. e. from 9-10 a. m. to 6-7 p. m. — and that little or 
no growth occurs at night. 
On comparing the curve of temperature we see that it does not explain the ups 
and downs of the upper curve ; maximum growth occurs with falling temperature. 
