6;o GENERAL CONDITIONS OF PLANT-LIFE. 



chlorophyll depends on conditions which favour assimilation, and that assimilation 

 proceeds vigorously in light transmitted through potassium bichromate, and consists 

 therefore of red, orange, yellow, and to a certain extent green rays ; while the 

 more strongly refrangible half of the spectrum, consisting of green, blue, violet, 

 and ultra-violet rays, obtained by passing the light through ammoniacal copper 

 oxide, has only a very slight effect. The conclusion at once followed from this, 

 that the formation of starch must take place in the set of rays first named to the 

 same extent that it does in full sunlight, but only to a very small extent in the 

 latter set. This was confirmed by Famintzin's experiments \ in which he found 

 that in Spirogyra the formation of starch in the chlorophyll took place only in the 

 mixed yellow light (that had passed through potassium bi-chromate), and not in 

 the mixed blue light (that had passed through ammoniacal copper oxide), in which 

 the starch already formed even disappears. Since however a small exhalation of 

 oxygen takes place even in the mixed blue hght, it must be supposed that a small 

 production of starch occurs in it. Kraus's experiments ^ with Spirogyra, Funaria, 

 and Elodea, confirm this. He also found that in plants of Spirogyra which had lost 

 their starch from exposure to dark, the formation of this substance in the grains of 

 chlorophyll recommenced in five minutes in direct sunlight, in two hours in diffused 

 daylight. In funaria the formation of starch recommenced in the same manner 

 within two hours in direct sunlight, within six hours in diffused daylight ; and 

 similar results were obtained from leaves of Elodea, Lepidium, and Betula^. 



(2) Mechanical Action of Light on Plants, (d) The influence of light on the 

 movement of protoplasm varies according to the nature of the motion. Those 

 movements which are the cause of the formation of new cells are not in general 

 directly dependent on light (see p. 673) ; since they take place, in the great majority 

 of cases, in partial or complete darkness. The ' streaming ' motion of the proto- 

 plasm in older cells, or rotation and circulation, also goes on in continuous dark- 

 ness as well as in alternate davli^ht and nio^ht : and even in the hairs of etiolated 



^ Famintzin, Action of Light on Spirogyra; Melanges biologiques, Petersburg 1865, Dec; and 

 1867, P- 277. 



'^ Kraus, Jalirb. fiir wissensch. Bot. vol. VII, p. 511. 



^ In accordance with the theory propounded by me that the starch formed in the chlorophyll- 

 grains under the influence of light is the first product of assimilation produced by the decom- 

 position of carbon dioxide, Godlewski has found (Flora, 1873, p. 383), as the result of experiments 

 as simple as ingenious, that in an atmosphere devoid of carbon dioxide no starch is produced in the 

 chlorophyll-grains even in the dark ; that the starch contained in the chlorophyll disappears when 

 the carbon dioxide is removed from the surrounding atmosphere, not only in the dark, but even in 

 bright light. It may be inferred from this that the starch which is at any time found in the chloro- 

 phyll is only the excess of the whole product of assimilation which has not yet been taken up. Of 

 especial importance is his observation, which agrees with his eudiometrical experiments, that an 

 increase in the proportion of carbon dioxide in the atmosphere to 8 p.c. in a bright light increases 

 the rapidity of the formation of starch four or five fold, while in a diffused light the action is much 

 less. A very large quantity of carbon dioxide in the atmosphere, on the contrary, retards the form- 

 ation of starch in inverse proportion to the intensity of the light. Godlewski's experiments, made on 

 the cotyledons of seedlings of Raphanus sativtis, are also opposed to the statement of Bohm (Sitz- 

 ungsber. der Wien. Akad. March 6, 1873), that the starch contained in the chlorophyll is not a 

 product of assimilation, a view which has already been sufficiently refuted by my earlier investi- 

 gations. 



