USE OF THE SPECTROSCOPE IN STUDY OF PLANT LIFE. 



95 



the same process as in a candle burning, energy in the form of hght 

 and heat is evolved, with CO2 and water.'-' 



The stimulus for respiration is not light, per se, though light may 

 be converted into heat, but the obscure heat-rays beyond the visible 

 red end of the spectrum. 



It has been found by experiments that, when plants are subjected 

 to gradual increments of temperature in total darkness, the amount 

 of CO2 gi^'en off increases proportionately with the increased degrees, 

 so that a curve drawn is a parabola, f This signifies that there is no 

 cessation until death ensues; though the optimum temperature is 

 750 to 850 F. 



It has been lately shown that colours in plants, other than the green 

 of chlorophyll, are, primarily, means of respiration; in that there are 

 "enzymes" or ferments wdiich are called "oxydases.":): These 

 respiratory enzymes (not acting directly upon the hydrocarbons), 

 oxidize the " chromogenes " — i.e. " colour-begetters," which thereby 

 become pigmented or coloured solid or liquid bodies. 



It is these chromogenes, enriched by the oxygen of the oxydases, 

 which now oxydize the hydrocarbons and fats. 



To show how extended the chromogenes are, if a potato or apple be 

 cut in halves and exposed to the air, the oxygen soon turns them brown. 

 Some fungi (as Boletus luridus) turns blue. 



The red colouring of living autumn leaves, as of Mcihonia, is due 

 to an accumulation of respiratory pigments. Eed sea- weeds, which live 

 in the deeper zones below low- water of our shores, have green chloro- 

 phyll, but it is masked by the red fluid. If they be scalded, the green 

 becomes visible. Now, the light which reaches the sea-bottom is mainly 

 blue-green, the other rays having been absorbed by the water, but, as 

 blue rays§ are also capable of bringing about photo-synthesis as well 

 as red and red-orange, the chlorophyll can utilize the forrner. But as 

 to respiration, it would seem that the use of the coloured fluid is to 

 act as an oxygen carrier, by some means extracting it from the air 

 in the water, for, as oxygen is so greatly reduced in quantity compared 

 with that in the atmosphere, sea- weeds, like fishes, might be called 

 " cold-blooded," the coloured pigment acting as an assistant to respira- 

 tion which is probably much feebler than in aerial plants. 



Perhaps a similar interpretation may be given of the fact that red, 

 purple, and blue pigments are very general in the foliage of high alpine 

 and arctic plants, which are mostly deficient in starch, but have sugar 



* To see the water, let a cold spoon be held over and close to the tip of the 

 flame. Visible moisture is at once condensed upon it; but, of course, it will be 

 quickly dissipated by the heat. 



t See article by MM. Bonnier et Maugin on " The Eespiration of Leaves in 

 Obscurity," Annates des Sciences Naturels, xix. 1884, p. 253; ibid. 6th ser. xvii. 

 p. 267. 



X An article on the presence of Oxydases and Peroxydiastases in seeds will 

 be found in Revue Generale de Botanique, vol. xxi. 1909, p. 55. Also one on 

 " The Distribution and Formation of Respiratory Chromogens," op. cit. p. 124. 



§ As I have elsewhere shown — Journ. R.H.S. 1893, *' On the Effects of Grow- 

 ing Plants under Glasses of Different Colours." 



