^50 GENERAL CONDITIONS OF PLANT-LIFE, 



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 chlorophyll-granules 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 chlorophyll-granules 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 chlorophyll-granules 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 chlorophyll-granules 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-granules 

 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- 

 granules 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 

 chlorophyll-granules 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 prothallia of Ferns and leaves of SagUtaria). Frank brought under a general 

 point of view the changes in position of the chlorophyll-granules 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 Epistrophei the protoplasm and chlorophyll-granules collect 

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

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

 (the leaves of SagUtaria^ Vallisneria, and Eloded) ; on the upper and under walls in 

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

 and in internal cells on the parts that bound the intercellular spaces. 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 conditions ; 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 



^ Bohm, Sitzungsber. der Wien. Akad. 1857, p. 510. — Famintzin, Jahrb. fiir wissensch, Bot. 

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

 "^ Prillieux, Compt. rend. 1870, vol. LXX. p. 60. — Schmidt, /. c. 

 ^ Frank, Bot. Zeitg. 1872, Nos. 14, 15; and Jahrb. fiir wissensch. Bot. vol, VIII. p. 216 et icq. 



