ACTION OF LIGHT ON VEGETATION. 67 1 



shoots which are developed in darkness \ It has not been ascertained whether 

 in these cases the rapidity and direction of the movement, the mode of distri- 

 bution of the currents, and the accumulation of the protoplasm at particular spots, 

 are influenced by the direction of the rays of light. An influence of this kind is 

 apparently exercised by light on the plasmodia of Aethalium. As long as the 

 Plasmodia are still in motion and not ripe for the production of spores, they appear 

 on the surface of the tan when it is dark ; but in the light, as in a sunny window, 

 they again conceal themselves in the dark parts of the tan, — a process which the 

 plant may be made to repeat two or three times in a day. It is not till the 

 Plasmodium has collected into a thick firm mass, and is preparing for the produc- 

 tion of spores, that it comes to the surface in places exposed to light, but appa- 

 rently only in the night or early morning. 



The protoplasm which envelopes the grains of chlorophyll in the green leaves 

 of Mosses and Phanerogams and in the prothallia of Ferns, is induced, by the 

 varying intensity of the light, to accumulate to a greater or less degree at different 

 parts of the cell-walls, carrying the grains of chlorophyll along with it, and thus 

 altering their distribution in the cell. It is still uncertain whether in this case the 

 light affects the protoplasm only, the grains of chlorophyll being carried passively 

 along with it ; or whether the influence of the light is not first of all on the latter, 

 which then give the impulse to the protoplasm. In either case it appears certain 

 that the grains of chlorophyll do not of themselves possess any power of free 

 motion, but are carried about by the motile protoplasm. Famintzin and Borodin^ 

 found that under the influence of continued partial darkness the chlorophyll-grains 

 in various Mosses and in the prothallia of Ferns collect on the side-walls of the 

 cells (those at right angles to the surface of the organ) ; and that when these parts 

 are exposed to light they leave them and distribute themselves over the parts of the 

 cell- walls which are parallel to the surface of the organ. Prillieux^ and Schmidt 

 have confirmed these statements. The view which I adopted long ago (see the first 

 and second editions of this work), that these changes of position in the chlorophyll- 

 grains are caused by the protoplasm, is confirmed by Frank's recent researches'*. 

 He shows that when the light falls only from one side, the protoplasm and the 

 grains of chlorophyll collect mostly on those parts of the cell-walls on which the 

 strongest rays fall, if the cells are sufficiently large to allow the light to be so 

 arranged, and these changes to take place in the position of their contents (as in 

 the prothaUia of Ferns and leaves of Sagittaria). Frank brought under a general 

 point of view the changes in position of the grains of chlorophyll described by 

 Famintzin and Borodin; he shows that the protoplasm in these cells is capable, 

 according to circumstances, of adopting two different modes of distribution. In one 

 mode, which he calls Epistrophe, the protoplasm and chlorophyll-grains collect on 

 the free cell-walls, z.e, those which do not immediately adjoin other cells; for 



^ Sachs, Bot. Zeitg., 1863, Supplement. 



2 Bohm, Sitzungsber. der Wien. Akad. 1857, p. 510.— Famintzin, Jahrb. fiir wissenf.ch. Bot. 

 vol. IV, p. 49.— Borodin, Melanges biologiques; Petersburg, vol. VI, 1867. 



3 Prillieux, Compt. rend. 1870, vol. LXX, p. 60.— Schmidt I.e. 



* Frank, Bot. Zeitg. 1872, Nos. 14, 15 ; and Jahrb. fur wissensch. Bot. vol. VIII, p. 216 et sej. 



