ACTION OF LIGHT ON VEGETATION. 75l 
and chlorophyll-granules collect chiefly on the walls that are not free, t. e. on those 
adjacent to other cells. The occurrence of apostrophe under direct sunlight which 
Borodin asserts^ (in various Phanerogams, as Lemna^ Callitriche, and Stellaria), is 
denied by Frank, who maintains that what takes place in these cases is rather a 
collection of the protoplasm at the spots where the light is strongest, which may 
happen to be at the sides^. 
It is evidently these aggregations of chlorophyll-granules on the side-walls of 
the cells caused by sunlight which were observed by Borodin that produced the 
phenomenon pointed out by Marquard and more exactly described by myself^, 
viz. that green leaves {e.g. those of Zea^ Pelargonium, Oxalis, Nicotiana, &c.) when 
exposed to sunlight assumed a bright green colour in a shorter time than in 
diffused light or in deep shadow. This can be made very evident by shading 
particular parts by pressing closely on them a strip of lead or tinfoil ; if this 
strip is removed after five or ten minutes, the parts that were shaded show a 
dull green, those exposed to the sun a bright green colour. It is obvious that the 
tissue will appear to the eye a deeper green in proportion as the green granules are 
distributed uniformly over the surfaces facing the eye, a less deep green in propor- 
tion as they collect on the side-walls. Borodin's observations directly confirm this 
hypothesis. This alteration in the grouping of the chlorophyll-granules which 
accompanies a change in the intensity of the light is caused only by the highly 
refrangible rays; the less refrangible rays (the bright and red ones) have the same 
effect as darkness*. It results therefore, as I showed in 1859, that if a strip of 
blue glass is laid on a leaf exposed to sunshine, it will produce no change of colour, 
while one will be caused by a strip of red glass. 
Since these movements of the chlorophyll-granules are produced by the 
colourless protoplasm in which they are imbedded, it might be expected that the 
protoplasm of hairs v/hich contain no chlorophyll or only a small quantity would 
be similarly influenced by the colour and intensity of the light. But the state- 
ments of Borscow and Luerssen^ which might be interpreted in this direction at 
least to some extent have not been confirmed by the observations of Reinke*'. 
The swarming of zoogonidia is also connected with protoplasmic movements. 
Their motile organs, the cilia, are supposed to be slender threads of protoplasm, by 
the vibration of which both the rotatory and the advancing movement of the zoogo- 
nidia is caused. The axis of rotation becomes subsequently the axis of growth ; the 
anterior end in the advancing motion (where the zoogonidium is usually narrower, 
^ Borodin, Melanges biol., Petersburg 1869, vol. VII. p 50. 
^ [From Stahl's investigations it appears that apostrophe is produced by direct sunlight (Bot. 
Zeitg. 1880). He finds that exposure to diffuse daylight produces epistrophe, that is, the position of 
the chlorophyll-granules in which the greatest area of their surface is exposed to the incident rays, 
whereas sunlight produces apostrophe, that is, the position in which the least possible area of their 
surface is exposed to the incident rays. In the one case they present their flat surfaces, in the other 
their edges to the incident rays.] 
2 Sachs, Berichte der math.-physik. Klasse der k. sächs. Ges. der Wiss. 1859. 
* Borodin, I.e.; Frank, Bot. Zeitg. 1871, p. 238. 
^ Borscow, Melanges biol., Petersburg 1867, vol. VI. p. 312. — Luerssen, lieber den Einfluss des 
rothen u. blauen Lichts u. s. w., Di.'-sertation, Bremen, 1868, 
® Reinke, Bot. Zeitg. 1871, Nos. 46, 47. 
