110 COLOUB. 



green, but no appreciable quantity of oxygen was 

 evolved ; and Humboldt grew the Lepidium sativum in 

 the light of a single lamp, and the green colour was de- 

 veloped. That colour is produced by the immediate 

 influence of light upon the coloured part is untenable 

 in such cases as follow. Wydler showed that in a 

 sea- weed taken from a very considerable depth, its inner- 

 most parenchyma was of a green colour ; the embryos 

 of Rhamneae and Malvaceae are green ; and the same 

 colour is seen in the structures immediately surrounding 

 the pith, etc., etc. ; and further, our knowledge upon the 

 subject is rendered more doubtful by the fact that cer- 

 tain plants which generally grow in the shade, and there 

 produce a green colour, when exposed to more light 

 evince a state of etiolation. Aspidium patens, etc., had 

 their fronds quite pale on the spots upon which beams of 

 light fell, whilst the other portions which were protected 

 from them continued green. 



143. That these and similar facts might be so resolved 

 as to tally with the general rule before laid down, 

 seems to me notwithstanding, highly probable, when we 

 take into consideration that the various processes of nu- 

 trition are, as a general body, modified in different mem- 

 bers of the vegetable kingdom, and that the amount of 

 stimulus necessary to call into play the vital actions of 

 these different members also varies ; and moreover that 

 we are equally deficient in a knowledge of many of the 

 conditions under which respiration and the nutritive 

 functions may and do take place, and with which a rela- 

 tionship in regard to the development of colour is sought 

 to be established. 



144. In respect to the chemical theory of colour in 

 plants, several opinions exist ; but we shall only notice 

 the views of Macquart upon the subject. 



145. The peculiar matter forming the green colour 

 resulting from the modifications that carbon undergoes, 

 and from whose various alterations all other colours in 

 plants arise, is denominated Chlorophyll. This substance 

 is soluble in the fixed and volatile oils, alcohol, and 



