Compounds in Chloroplasts of Green Cells of Plants. 559 



Now the chloroplast contains a great deal more than chlorophyll, and when 

 all the chlorophyll has been removed by some such reagent as hot alcohol 

 there remains behind a colourless body, the so-called stroma. The chloro- 

 plast after the extraction is still a solid looking body, and to all 

 appearances the only thing that has happened is that a thin layer of green 

 colouring matter has been removed. There is no shrinking or shrivelling up 

 of the chloroplast. 



There is accordingly no experimental evidence that the primary agent in 

 the photo-synthesis may not be contained in the colourless part of the 

 chloroplast, and the chlorophyll may be evolved at a later stage in synthetic 

 operations induced by some constituent of the colourless part. The function 

 of the chlorophyll may be a protective one to the chloroplast when 

 exposed to light, it may be a light screen as has been suggested by 

 Pringsheim, or it may be concerned in condensations and polymerisations 

 subsequent to the first act of synthesis with production of formaldehyde. 



All these views and others are possible, and the function of chlorophyll in 

 the chloroplast remains for solution, but it has not been proved that 

 chlorophyll is the primary causative agent in the photo-synthetic process 

 where the chief energy uptake occurs with formation of formaldehyde. 



There are other pieces of experimental evidence apart from the repeated 

 failures to obtain satisfactory synthesis with isolated chlorophyll which go 

 to indicate that chlorophyll is not the transformer in the first link of the 

 synthetic chain. 



In the first place chlorophyll itself is a product of photo-synthesis, and 

 therefore there must be some active photo-synthetic substance present in 

 the chloroplast before the chlorophyll appears which indeed first produces 

 the chlorophyll by its activity. 



When a yellow etiolated leaf taken from the darkness is exposed to the 

 light it contains no chlorophyll, but photo-synthesis, in the absence of 

 chlorophyll, sets in, and chlorophyll itself is one of the products, not the 

 originator or agent, of this photo-synthesis. The period from first exposure 

 to light to the appearance of chlorophyll is too short to determine whether 

 oxygen production and starch formation commence before chlorophyll is 

 formed. 



In the next place Engelmann,* by the application of his ingenious method 

 of the oxyphile bacteria has clearly demonstrated two important facts : 

 first, that the chloroplast alone, even when displaced from the rest of the 

 cell, can, in presence of light, go on synthesising and producing oxygen ; 



* ' Botanische Zeitung,' 188], p. 446, and 1887, pp. 394, 410, 418, 426, 442, 458. 



2 U 2 



