67Z GENERAL CONDITIONS OF PLANT-LIFE. 



instance, next the surface in the superficial cells of organs consisting of several layers 

 (the leaves of Sagittaria, Vallisneria, and Elodea) ; on the upper and under walls in 

 organs consisting of only one layer of cells (leaves of Mosses, prothallia of Ferns) ; 

 and on the parts that bound the intercellular spaces in internal cells. This is 

 the position assumed in the normal conditions of vegetation and the mature state 

 of the cells, but before they become too old. The second mode, or Apostrophe, 

 takes place under unfavourable external condidons ; as for instance in small 

 fragments of tissue, when respiration is defective, turgidity diminished, the tem- 

 perature too low, the cells too old, or — what is of most interest here — when light 

 is cut off for a considerable time. Under these circumstances the protoplasm 

 and chlorophyll-grains collect chielly on the walls that are not free, i. 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- grains on the side-walls of the 

 cells caused by sunlight which were observed by Borodin that produced the phe- 

 nomenon pointed out by IMarquard 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 grains 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 grains of chlorophyll which 

 accompanies a change in the intensity of the light is caused only by the highly 

 refrangible rays ; the less refrangible ra}'S (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 grains of chlorophyll are produced by the 

 colourless protoplasm in which they are imbedded, it might be expected that the 

 protoplasm of hairs which 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 conflrmed by the observations of Reinke ^. 



^ Borodin, Melanges bid., Petersburg, 1S69, vol, VII, p. 50. 

 ^ Sachs, Berichte der math.-physik. Klasse der k. sJichs. Ges. der Wiss. 1859. 

 ^ Borodin, I.e.; Frank, Bot. Zeitg. 1871, p. 238. 



* Borscow, Melanges biol., Petersburg 1867, vol. VI, p. 312.— Luerssen, Ueber den Einfluss des 

 rothen u. blauen Lichts u. s. w.. Dissertation, B:emen, 1S68. 

 5 Reinke, Bot. Zeitg., 1871, Nos. 46, 47. 



