6 STUDIES IN GENERAL PHYSIOLOGY 
direction of the rays, to or from the source of light. The 
more refrangible rays alone exercise this effect on the swarm- 
spores. They behave in the light which has passed through 
an ammoniacal solution of copper just as in diffuse daylight. 
On the other hand, they are not affected by light which has 
passed through a potassium bichromate solution, by light 
from a sodium flame, or by the light coming through ruby 
glass. 
The chlorophyll-bearing protoplasm of cells moves under 
the influence of light.'’ The chloroplasts of a thread alga, 
Mesocarpus, turn ‘their broad surfaces toward the sky so that 
the rays fall upon them at right angles. If the direction of 
the rays is changed, the chloroplasts turn so that their broad 
surfaces are again at right angles to the rays. Direct sun- 
light, however, causes the chloroplasts to assume another 
position—they place their surfaces parallel to the rays which 
strike them.” 
According to modern plant physiology, the whole proto- 
plasm of a multicellular plant is to be conceived of as a 
continuous mass, as a single protoplasmic body.? More 
recent investigations have shown that when a plant organ is 
illuminated, that side of the organ which becomes concave 
from the effect of the light becomes rich in protoplasm, while 
the opposite convex side becomes poor.’ Multicellular organs 
behave in this regard like unicellular ones. Thus it appears 
that the light forces the protoplasmic mass to move in such a 
way that positively heliotropic protoplasm wanders to the 
side of the organ which is turned toward the light, while 
negatively heliotropic protoplasm wanders to the opposite 
side.’ Should it turn out that this phenomenon really oceurs 
1STAHL, Botanische Zeitung, 1880. 2 Sacus, loc. cit., p. 94, 
3 Wortmann expressed his observations in this way. It is possible that in 
reality protoplasm on the concave side is only more opaque than on the opposite 
side. This difference in optical appearance may simply be the expression of a 
difference in the size of the colloidal particles. 1903] 
+See WorTMANN, Botanische Zeitung, 1887. 
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