CHAP, ii Photosynthesis 297 



veloped gradually from the time when Sachs called attention 

 to the fact that ' growth of the organs and assimilation in 

 the chlorophyll are two processes mutually independent in 

 a high degree ' (Lectures on the Physiology of Plants, Eng. 

 ed., p. 300). In 1881 Engelmann discovered that an 

 isolated plastid can effect a little decomposition of carbon 

 dioxide. In 1887 Haberlandt made a still more explicit 

 statement on this point, based on observations of the 

 behaviour of the plastids of Funaria hygrometrica in a 

 25 per cent, solution of sugar. Ewart also, nine years later, 

 established the accuracy of the observations of his pre- 

 decessors. He investigated a number of plants, cutting 

 sections of their leaves in sugar solutions of various con- 

 centrations. Many plastids escaped from the cut cells, and 

 he placed them on slides in sugar solution and added 

 numbers of the organism Bacterium termo taken from pure 

 cultures. Great precautions were observed in order to 

 exclude all traces of other organisms, such as small uni- 

 cellular Algae, which are not uncommon on moss leaves. 

 The preparation being made with all due care, Ewart 

 closed the cells hermetically and waited. In some cases 

 movements of the bacteria indicated that oxygen was being 

 given off ; in others there was no result. The best results 

 were obtained when the plastids were quite free from any 

 debris of plasma from the cut cells. The plants with which 

 positive results were obtained were Catherinea undulata, 

 Fimaria hygrometrica, Dicranum scoparium, Vallisneria 

 spiralis, and Selaginella helvetica. 



Engelmann obtained similar results with the green cells 

 or plastids which he was able to isolate from the body of 

 Hydra viridis. Whether or no these are to be regarded 

 as chloroplasts is, however, disputed. Most zoologists 

 regard them as Algae living in some kind of symbiosis 

 with the Hydra. 



The balance of evidence is therefore in favour of the view 



