530 Smith . — The Temper ahtr e-coefficient of 
Take first Blackman and Matthaei’s Expt. X. The experimenters’ statement 
is as follows : 
‘ For the first four readings the temperature was kept down to about 
1 8°, and again in the last two the temperature was the same. In all these 
readings except the first, which was low, due to the extremely overcast 
leaden sky, the assimilation numbers are remarkably uniform, 0*0089, 
0*0090, 0*0089, 0*0089, 0*0092 ; while the light varied up and down, being 
especially brighter in the last two readings. This can only be interpreted 
as being due to the fact that the assimilation is limited by the temperature, 
which has been kept steady throughout. Striking confirmation of this is 
obtained by raising the temperature for the fifth reading. The sky was 
7 io lighter than before , but yet, on the temperature being brought up to 
30*5°, the assimilation at once doubled, becoming 0*0163.’ 
In Expt. XI it is shown that the same assimilation value is obtained 
at the sixth reading as at the first, although the light was much brighter at 
the sixth reading. This can only be due to the controlling influence of 
temperature, as claimed by Blackman and Matthaei. 
In Expt. XVI also, two readings were obtained at a temperature 
of 30°, in the second of which a considerable proportion of the illumination 
was cut off by a wooden tube, yet the assimilation did not fall, proving that 
temperature and not light was the limiting factor. 
When there are provided these definite proofs in each experiment that 
the temperature was the controlling factor, of what scientific avail is Brown 
and Heise’s statement that they would prefer to attribute all the changes to 
variations in illumination ? 
In their final discussion of the temperature-coefficient of assimilation 
Brown and Heise have attempted to show that its value is 1*04 + 0*03, i. e. 
that assimilation is practically unaffected by temperature. They claim that 
this value is supported by the results of the investigators named in 
their Table I. 
Name of Investigator. Name of Plant used . ^ndHdse^ 
Matthaei Cherry-laurel 1.0 + 
Prjanischnikow Typha i.o + 
Kreusler Rub?is 1.16 
Blackman and Smith Elodea 1-35 
van Amstel Elodea 1.26 
The results of all these workers have now been reviewed in this paper 
with the exception of those of Prjanischnikow ( 1876 ), which are not 
sufficiently accurate in method to merit discussion in this connexion, and it 
has been shown that the only accurate and trustworthy values for the 
coefficient are those of Matthaei on Cherry-laurel, which is 2*1 ; of Blackman 
and Smith on Elodea , which is 2*05; and of Blackman and Matthaei on 
Helia 7 ithis , which is not definitely given, but is probably about 2*5. All 
