INVESTIGATORS IN PHOTOSYNTHESIS 67 



the phenomenon is that the leafy shoots give off oxygen 

 in light and carbon dioxide in darkness, while non-green 

 parts give off carbon dioxide both in the light and in the 

 dark. From the carbon and oxygen the plants construct 

 " acids, oils, mucilage, etc.," and these bodies are then 

 combined with the nitrogen of the air. This latter idea 

 is of course erroneous, but it took another fifty years to 

 prove it so. That, unfortunately, was not the only 

 blunder he made. Although he admits that the leaves 

 absorb carbon dioxide he still thinks that a considerable 

 proportion is obtained by the roots from the soil. He 

 also falls into the error of beUeving that the plant gets 

 its oxygen from the carbon dioxide by night and in the 

 shade, and carbon from the same source in sunlight, 

 giving off the oxygen and retaining the carbon as a 

 nutrient. I cannot find in Ingen-Housz's pages any 

 justification for Sachs' statement that he " not only 

 discovered the assimilation of carbon and true respiration 

 of plants but also kept the conditions and the meaning 

 of the two phenomena distinct from one another." But 

 even if we do not credit him with all that Sachs claims 

 for him, we must admit that Ingen-Housz is fully worthy 

 of a place in the front rank of those who laid the founda- 

 tions of our knowledge of plant nutrition. 



A contemporary of Ingen-Housz was the Swiss botanist 

 Senebier, who in the eight years between 1782 and 1790 

 published a series of treatises on the subject of plant 

 nutrition. The Memoires appeared in 1782 ; the 

 Recherches in 1783 ; the Experiences in 1788, and the 

 Physiologie vegetale in 1790. Senebier recognised that 

 leaves are essential organs to all plants which possess 

 them, but he expressed astonishment that some plants 

 have no leaves and yet, having green stems, give off oxygen 

 in sunhght, thus missing the important generalisation 

 that function need not be dependent on morphological 

 value. Many of Senebier's conclusions are merely 

 restatements of those of Ingen-Housz, with whom he 



