520 BOTANICAL GAZETTE [DECEMBER 
temperature of the leaf is usually higher than that of the air. If, however, 
the temperature of the leaf falls lower than that of the air, the leaf will gain 
energy from the air, that is, thermal emission will be negative. Brown and 
EscoMBE’s values for thermal emission are based on the same set of experiments 
as the data quoted under (2), (3),and (4). They areall positive. The smallest 
one is 6.0 and the largest is 54.60 per cent. Brown and EscomBe were the 
first to attempt to obtain a complete balance sheet for the leaf in regard to 
energy. Further quantitative data correlating the work of BLACKMAN, 
BRown and EscomBe, and PurIEwItTscH are greatly to be desired. We still 
have no reliable data on which any conclusion can be based as to the relative 
efficiency of the rays in the different portions of the spectrum. 
e reviewers mention the early work, indicating that the maximum 
assimilation takes place in the red part of the spectrum and that there is a 
secondary maximum in the blue-violet end as being now of only historical 
interest, since the methods of measuring energy were unsatisfactory and the 
measurements of assimilation were crude. 
The work of Knrep and MinbeEr (1909), indicating that blue and red light of 
the same intensity produce the same assimilation and that the green light is 
incapable of producing assimilation, is rejected because they give no data 
relating to any factors other than light intensity, hence some other factor may 
have been a limiting one. They also reject TIMIARIZEFF’S (1903) data on 
the absorption of energy by chlorophyll, since he worked with alcoholic extracts, 
which must have contained less chlorophyll than impurities. The work of 
Brown and EscomseE on the absorption of radiant energy by the white and the 
green portion of a leaf of Negundo aceroides is also rejected, since it is considered 
unfair to assume that the conditions in the green and the albino parts are the 
same except for the presence of chlorophyll. Werr1cERT’s (1911) conclusions 
on the efficiency of the assimilation system are considered unreliable, since they 
are based on the work of Brown and EscomBe just mentioned. 
The reviewers introduce their discussion of theories of carbon assimilation 
with a sweeping condemnation of theories, making the point that those who 
have contributed the most valuable data on this subject have not suggested 
any theories. They cite DE SaussurE, SAcHS, PFEFFER, and BLACKMAN as 
examples. They might possibly have added SpoenR to the list, but they 
could not have added WittstAtrer, since his data on the pigments of the 
green leaf are certainly very eS pas considerable space is given in their 
review to the discussion of his theor 
course blind following of a fa does not lead to progress, and the 
desirable attitude is that of seeking for facts regardless of their bearing on 
any theory, but to assume that none of the workers (except SPOEHR) have 
been influenced by dissatisfaction with the theories that have been advanced 
seems unwarranted. It is not the right use of scientific imagination that is to 
be condemned, but the acceptance of mere imaginings as facts. JORGENSEN 
and StiLes, of course, are quite right in their condemnation of whatever 
