96 Dr. H. T. Brown and Mr. F. Escombe. [Jan. 9, 
If the transmission through the albino-leaf is taken as 100, that of the 
ereen leaf will be represented by 83:5, a difference of 16°5 per cent., which 
may be regarded as expressing the increase in the absorptive power due 
to the colouring matters of the leaf. 
In connection with the increased absorption induced by the leaf-chlorophyll, 
it is of interest to compare the above results with those of Timiriazeff, which 
were obtained by a totally different method.* 
Timiriazeff’s mode of procedure was to punch out of a leaf a circular piece 
of known area, and to dissolve its green colouring matter in a volume of 
alcohol just sufficient to fill a glass cell.,of exactly the same cross-section 
as the area of the leaf. The absorptive power of the coloured solution for 
the radiant energy of sunshine was then determined by means of a delicate 
thermopile, the absorption for the glass and solvent being ascertained 
separately. The difference between the two readings was taken as repre- 
senting the absorption due to the chlorophyll. 
Timiriazeff obtained by this method the following results for the absorption 
induced by the chlorophyll of single leaves. 
Absorption 
of direct sunlight. 
Maple oi, 5..0. 2 eee 27-0 per cent. 
Tele: 2 eae 290i ash, | 
Oa Rahs sacl oe ees peepee Darah pia 
Plantae. Ace ere DS Aay e 
Potamogeton —.02...242% 20°0 : 3 
The leaf of the Negunde was not included in Timiriazeffs experiments, but 
a consideration of his results points to the probability of this leaf showing by 
his method a chlorophyll-absorption of more than the 16°5 per cent., which 
was the amount we found by direct observations on the leaf-lamina. 
The widely different methods of experiment would account for this, since 
the chlorophyll when in solution is under more favourable conditions for 
exerting its maximum absorptive power than it is under the natural conditions 
which exist in the living leaf. In the latter case, owing to the particulate 
nature and scattered distribution of the chlorophyll-bodies, the transmitted 
radiation must be subjected to a less complete selective absorption than when 
the chlorophyll is in a state of solution. 
* See Croonian Lecture, ‘ Roy. Soc. Proc.,’ 1903, p. 449. 
