TKA>'SPIRAT10N OF PLA.NTS. 85 



In ascertaining the amount of transpiration induced by ditter- 

 ent rays of the spectrum, AVicsner adopted two methods : first, 

 by phicing the plant in certain rays of tlie spectrum it«elt'; and, 

 secondly, under coloured fluids. The results were mutually cor- 

 roborative. 



The following were the results by the first method ;- — Ked gave 

 1315 milligr. per hour j yellow-orange, 122 ; blue, 146 ; ultra- 

 violet, 70 ; obscurity, G2. He next compared these results with 

 others from leaves placed as accurately as possible in the parts of 

 the spectrum corresponding with the absorj^tion-bands of chloro- 

 phyll. These latter gave the following results : — 



Eed (with absorption-band No. I.) y4'3 milligr. per hour. 



Tellow^-orange (between bands II. and £11.) 32-0 „ „ 



Green (between IV. and V.) 30-4 



Blue (corresponding to band VI.) 38*7 



i> » 



>j V 



From this he concludes : — ^'11 est done bien evident que ce ne 

 sont pas les rayons les plus lumineux, les rayons jauiies, qui 

 iavorisent le plus la transpiration ; mais que celle faculte est 

 repartie dans tout le spectre, de telle maniere que les rayons les 

 plus actifs sont prejisement ceux qui correspondent aux sept 

 bandes noires du spectre de la chlorophylle. 



"II est curieux d'observer la plus forte transpiration dans les 

 rayons qui correspondent a la bande VI. M. von AVolkoff a 

 fait voir recemment* que c'est dans cette partie du spectre chlo- 

 rophyliien que se fait la plus jjuissante absorption de lumiere. 



"Les parties du spectre situees entre les bandes d'absorption, 

 et qui sont toujours plus on nioins obscurcies par le 2)assage a 

 travers une solution de chlorophylle, ne sont pas sans action sur 

 la transpiration ; mais cette influence est inferit ure a celle des 

 rayons completement eteints dans cette solution "f. 



That the presence of chlorophyll is intimately connected with 

 transpiration is clear from the difi'erent results obtained by 



to distinguish bet-ween the two processes evaporation and transpiration) is that 

 older leaves absorb more heat than the younger ones of the suuie kind, and 

 evergreens more tlion deciduous leaves; yet, according to Deherain, it is exactly 

 the reverse which transpire the most. Hence, if this function be identical with 

 the purely physical process of evaporation, it would be diiBeult to reconcile the 

 above fact with it. 



* * Die Lichtabsorplion in den Ghlorophjllog^ungen ; ' ITeidelLerg. '[^7(^. 



t Ann. Sci. Nat. per. 0, iv. (1^7()), p. 109. 



