ACTION OF LIGHT ON VEGETATION. 749 



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

 chlorophyll-granules under the influence of light is the first product of assimilation 

 produced by the decomposition 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-granules 

 even in the light; that the starch contained in them 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 chlorophyll-granules is only the excess of the whole product of assimi- 

 lation 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 con- 

 trary, retards the formation of starch in inverse proportion to the intensity of the 

 light. Godlewski's experiments, made on the cotyledons of seedlings of Raphanus 

 sattvus, are opposed to the statement of Bohm (Sitzungsber. der Wien. Akad. 

 March 6, 1873), that the starch contained in the chlorophyll -granules is not a pro- 

 duct of assimilation, a view which has already been sufficiently refuted by my earlier 

 investigations. 



(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. 752) ; 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 daylight and night ; and even in the hairs of etiolated 

 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 ^thaliu?ji^. 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 fight, as in a sunny window, 

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



Wurzburg, II. 2, 1879) ^^ appears that equal areas of the leaf-surface of different plants produce 

 different amounts of organic substance in a given time, the conditions being the same. He obtained 

 the following numerical proportion for the energy of assimilation : — 



Tropceolum mnjus ..... 4.466. 



Phaseohis muldflorus . . . . 3-215. 



Ricinus communis ..... 5.292. 



Helianlhus annuus . . . . . 6 •559'] 



* Sachs, Bot. Zeitg,, 1863, Supplement. 



* [This subject has been investigated by Baranetzky (Mem. d. 1. soc. nat. d. sci. nat. de Cherbourg, 

 XIX, 1876): he found that the plasmodia, whilst still young, always avoided light. Schleicher has 

 found on the contrary (Strasburger, Wirkung des Lichtes und der Warme auf Schwarmsporen, Jen. 

 Zeitschr. XII, 1878) that the young plasmodia seek the light when its intensity is small: older 

 Plasmodia seek the light even when it is very intense.] 



