76 SUMMARY OP CURRENT RESEARCHES RELATING TO 



decomposed, while in some cases there was even a decrease in the 

 evolution of oxygen. The author does not, however, conclude from 

 this that tlie same is necessarily the case for all plants. It is not 

 only possible, but even probable, that with certain plants the light 

 which reaches the chlorophyll-containing tissue, through the strongly 

 developed epidermis or other structures, is so weakened that the opti- 

 mum is not attained even in the brightest sunshine. 



2. Experiments with a gas-flame of an illuminating power of 

 about 50 candles, partly in air and partly in water containing CO2. — 

 A very considerable decomposition is eifected by this flame, on the 

 average about one-third of the amount effected by direct sunlight ; a 

 result quite in accordance with the existence of an optimum. The 

 existence of such an optimum of light-intensity for the evolution of 

 oxygen, is in all probability intimately associated with the well- 

 known changes of form and position of the chlorophyll-grains in 

 direct sunshine, by which they turn their narrow edge towards the 

 light, and thus diminish the amount of incident light. The estab- 

 lishment of this optimum is of great importance in exact experiments 

 on the influence of the various rays of light on the decomposition of 

 CO2, and offers some explanation of the results, which at present 

 appear contradictory. 



Decomposition of Carbonic Acid by Plants in Artificial Light.* 

 — In the year 1865, M. A. Famintzin experimented on the action of the 

 light of a creosine lamp on Svirogyra, and showed that if filaments of 

 the alga, from which the starch had disappeared from long immersion 

 in darkness, were exposed to the action of this light, grains of starch 

 again shortly made their appearance in the chlorophyll-bands. The 

 starch thus formed was assumed to be the product of the assimilation 

 of carbonic acid, although the evolution of oxygen was not experi- 

 mentally proved. In order to settle the doubt raised by Bohm, 

 Famintzin has now repeated the experiment with Spirogyra and other 

 plants, and proved the elimination of oxygen. 



Action of Light on the Formation of the Red Pigments in 

 Plants.t — Professor Batalin has obtained the following results from 

 experiments on germinating seeds of Polygonum Fagopyrum. Pure 

 white light is necessary for the formation of the pigment ; if decom- 

 posed, it is not sufficient ; the intensity of colour depending on the 

 degree of illumination. A small amount of light, less than is necessary 

 for the production of chlorophyll, is sufficient to initiate the formation 

 of the pigment, if with a minimum duration of from four to ten hours. 

 Under these conditions, a secondary coloration also takes place of seed- 

 lings grown previously in the dark ; but if they are entirely excluded 

 from light, they perish without turning red. A high temperature is 

 favourable to the formation of the pigment. Chromogen is stored up 

 in the axial structures, rhizomes, tubers, bulbs, &c. As the cells 

 increase in age they lose their capacity for producing the pigment. 



* Bull. Acad. Imp. Sci. St. Petersburg, xxvi. (1880) pp. 136-42; and Ann. 

 Sci. Nat. (Bot.), x. (1880) pp. 62-6. 



t Acta horti Tetrop., VI., ii. pp. 279-86. See Bot. Centialbl., 1. (1880) 

 p. 966. 



