1903.] The Cosmical Function of the Green Plant. 455 



of this area corresponding to the absorption spectrum of a single 

 chloroplast, and lastly the thickness of the layer of the colouring 

 matter in this chloroplast. 



The total amount of energy is established by Crova's, Langley's, 

 Savelieff's and other researches. I have myself made some evaluations 

 with. Crova's portable actinometer. I think we shall be nearest to the 

 truth by adopting the number 1, 3 calories per centimetre per minute. 



The fraction of the total energy corresponding to the absorption of 

 the chloroplast was obtained in the following manner. A Sorby- 

 Browning microspectroscope was used without its prism, simply as a 

 colorimeter, in order to obtain a solution possessing the same degree of 

 concentration of the colouring matter as in the chloroplast).* This 

 solution was then studied spectrophotometrically, using d' Arson val's 

 spectrophotometer in the way already described. 



Concerning the last point the thickness of the layer of colouring 

 matter I fear I shall be somewhat at variance with the current ideas 

 adopted by histologists. It is generally admitted that the green 

 colouring matter is distributed through the whole body of the proto- 

 plast, but many years ago Nageli, using the following very simple 

 expedient, proved that it is restricted to its surface. If water be added 

 to a preparation (Nageli used chlorophyll grains of Clivia and 

 Aspidistra), the chloroplasts burst, arid we may see that the green 

 shell or film has for the greater part the appearance of two valves. I 

 have many times repeated Nageli's experiment with the chloroplasts 

 of Phajus, which are far more convenient, being much larger. The 

 chloroplasts liberated from their cells are examined in a solution of 

 sugar, where their appearance is not in the least altered. On the 

 solution being diluted with water, at a certain moment they burst. 

 Adding some sulphate of copper we arrest the process, and obtain 

 durable preparations that may be dyed with Eosine and then present 

 a, very elegant object, somewhat recalling the bud of a pink poppy 

 with its bivalved calix. 



Another way of testing the distribution of the colouring matter is to 

 inspect the chloroplasts in red light; we may then see the so-called 

 gram as very small black specks in a very thin layer restricted to the 

 surface. If we try to estimate the thickness of this green layer or film 

 a strict measurement is out of the question we arrive at the 

 approximate value of ^ of a micron. 



Having obtained all these necessary data, we may arrive at our 

 rough estimate of the temperature that could be realised in a minute 

 in this layer of chlorophyll, admitting, of course, that the whole energy 

 would be accumulated without being re-radiated. We arrive at the 

 astounding figure of about 6,000 degrees. 



* In actual fact this concentration was reduced to one-half the reason for this 

 reduction will be seen hereafter, when the structure of the chloroplast is discussed. 



