CHLOROPHYLL THE AGENT OF ASSIMILATION. 299 



chlorophyll as a matter of fact, not as a proper constituent of the body, but, as 

 Brandt has recently shown, have vegetable cells (Algae) containing chlorophyll in 

 their bodies : by means of the assimilation of these green bodies, such animals may 

 be nourished under certain circumstances '. 



It matters little in what form the chlorophyll is contained in the cells : whether, 

 as is usual, in the form of soft granules, or, as in the Conjugateae (a group of Algae), 

 in the form of green bands or plates, or even simply as masses of protoplasm tinged 

 with green, as in the Palmellacem and some other Algae. It also makes no essential 

 difference whether or no other colouring matters besides the chlorophyll are present 

 in the cells, as in the red Algae (FloricUtE) or the yellow-brown Fucaceae. It was 

 a fatal mistake of De Saussure's to argue froin the red colour of many leaves, such as | 

 the red garden Orache (Atriplex hortensis), that chlorophyll is unnecessary for the 

 decomposition *of carbon dioxide : Cloez, in 1863, first insisted upon the presence of 

 chlorophyll even in such cases. The whole literature on the nutrition of plants, even 

 of twenty or thirty years ago, shows how ill established was the knowledge of the 

 fact that it is the chlorophyll only which effects the decomposition of carbon dioxide : 

 it was always the custom to say cautiously that green plants decompose carbonic 

 acid, without more exactly indicating which organ eflfects this decomposition. In 

 general, definite recognition of the fact that it is the chlorophyll which is the agent 

 for the decomposition of carbon dioxide has only made way since the appearance of 

 my ' Handbook of Experimental Physiology ' in 1865 ; and when a more recent author 

 finds that, properly speaking, it is not the chlorophyll but the cell containing chloro- 

 phyll which is the organ of assimilation, because the one is contained in the other, it 

 is somewhat equivalent to saying that the eye is not properly the organ of sight, since, 

 when taken out of the head, it is no longer capable of seeing. Since no cell assimi- 

 lates so long as it possesses no green chlorophyll, but does so as soon as it is provided 

 with it, we are justified in distinguishing the chlorophyll-body itself as the organ which 

 decomposes carbon dioxide, and consequently assimilates the organic substance. The 

 most definite proof, however, is afforded by the fact, to be stated more exactly further 

 On, that the first recognisable product of assimilation appears not in any haphazard 

 place in the cell containing chlorophyll, but in the chlorophyll-body itself. 



I have repeatedly taken the opportunity of referring in these lectures to 

 the essential co-operation of light in assimilation in the chlorophyll. We are 

 here in fact concerned with the dependence of plant-life upon the external world, 

 and in reviewing the different phenomena of vegetation this must never be lost 

 sight of, if the most mischievous errors are to be avoided. The great importance of 

 the fact that a plant containing chlorophyll, so long as it does not meet with light 

 of suflBcient intensity is not able to decompose carbon dioxide, and, therefore, is not 

 capable of producing organic substance of any kind whatsoever, must always be 

 kept in view. For those not familiar with vegetable physiology a misleading diffi- 

 culty arises in that plants, in spite of being in dark or feebly illuminated situations, are 

 able, according to circumstances, to continue living and even to grow vigorously for 

 some time, particularly when they are well provided with assimilated reserve-materials. 



' K. Brandt, ' Ueber das Zusatnmenhben von Thieren und Algen^ (Verhandl. der physiol. 

 Gesellsch. zu Berlin), Dec. 2, 1881. 



