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. 1 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. 2 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. 3 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. 4 Should it turn out that this phenomenon really occurs 



i STAHL,, Botanische Zeitung, 1880. 2 SACHS, 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. 



