342 
BOTANICAL GAZETTE 
[NOVEMBER 
cultures of Dictyota dichotoma under one-sided illumination, but 
with the ordinary alternation of daylight and darkness, I noticed 
that both the direction of divisions that took place at night and also 
the cell which put out the rhizoid did not conform to the rule to which 
those spores which germinated in the daytime evidently pointed. 
This is clear from figs. 17 and 18. Rhizoids, 
formed during the night on the side which 
did and will receive more light during the 
day, bendaway from the light when the day- 
Fics. 17, 18.—Dictyota 
dichotoma. X123. 
17. Germinating spores 1} 
days since sowing on ground 
t, direction. of light 
spores 1, 2, 3 divided during the 
night (in darkness), and that the 
rhizoids o are curving 
away from the light—18. Some- 
what older. 
such a polarity, for the undivided sp 
After the first division the spore becomes 
of the daughter cells at right angles to the divisi 
grow from one or the other end—sometimes from 
ellipses, not from the side; but beyond this there 1 
the point of origin of the rhizoid. So 
justified in saying is that, in the light, the 
spore and the point of origin of the rhizoid 
by the direction from which the light falls upon 
spore has the impulse both to divide and to 
do both even in the absence of any directive 
case the direction of division and the point 
are determined by conditions preceding the esca 
light comes. 
In such cultures as these we 
have much more nearly normal conditions 
than in continuous darkness or on the clino- 
stat. Divisions often occur and the rhizoids 
often grow out in ‘darkness, and though the 
spores were lighted only from one side during 
the day, the direction of these divisions and 
the side from which the rhizoid springs fol- 
low no rule. 
This fact at least suggests, 
but without proof, that influences preceding 
illumination 
also affect the direction 
division of the spores, and the point of 
origin of the rhizoids. 
* 
of origin of 
pe of the 
olarity in the spor 
spore that there 
on wall. The rhizsids : : 
