518 BOTANICAL GAZETTE [DECEMBER 
In discussing WILLSTATTER’S work on the relation between chlorophyll 
content and assimilation rate, the reviewers state that “‘ WILLSTATTER advances 
a simple definite $e dienes and tama 0 obtain spcteaesrnat sae —— 
will support his theory arbo ti 
sists of two definite paeceen, one photochemical, taking place in the dito: 
roplast, and one enzymatic, taking place at the boundary between the 
chloroplast and the plasma. nee cnyeen is supposedly ee during the 
latter process. te. The view 
is not a surprising one, however, since the relation of carbon assimilation 
and of enzymatic action to temperature both seem to be special cases of 
TamMaAn’s principle. The surprising thing would be that there should be only 
two processes concerned. The reviewers state that under certain circum- 
stances, when no other factor is limiting, the amount of chlorophyll determines 
the intake of CO. by the leaf. WutisTATTER found th the amount of pigment 
is not altered during the process of carbon assimilatio 
he discussion of the present status of our ister of the known products 
of assimilation (oxygen and carbohydrates) is based on the work done within 
the last 31 years, since the earlier workers did not separate the gaseous ex- 
changes due to assimilation from those due to respiration. It seems probable 
that the real assimilation coefficient (taking respiration into account) approxi- 
mates unity. In considering the nature of a reaction or a series of reactions, it 
is very important to know the quantitative relation between initial substances 
and the final products of the reaction. In carbon assimilation by green leaves 
the relation between CO, taken in and O, evolved has not been definitely 
established 
The reviewers summarize in a table (p. 106) the evidence in regard to the 
presence of various carbohydrates in the leaf. (1) Polysaccharides (exclusive 
of cellulose and pectic substances); the presence of starch has of course long 
been well known, and the presence of pentosans and dextrin seems to be 
established. (2) Disaccharides; sucrose is certain, and maltose is doubtful. 
(3) Hexoses; the presence of d-glucose and d-fructose is well recognized. 
(4) Pentoses; none are positively known to be present, although there is some 
evidence pointing to the presence of l-arabinose and J-xylose. Definite evi- 
dence as to what sugars are absent and more quantitative data in regard to the 
ones present are much to be desired. The reviewers state that there is strong 
evidence that sugars are the first definitely known products of the assimilatory 
process, starch probably being a secondary product. Although most workers 
regard cane sugar as first, there is no satisfactory evidence that the hexoses may 
not be first. The mechanism of translocation is complex, depending upon 
differences of enzyme concentration, and possibly upon permeability changes, 
the nature and causes of which are at present largely unknown. The available 
data on energy relations are dealt with under three heads: (1) quantitative 
determinations of materials produced and their heats of combustion, (2) meas- 
urement of both radiant energy and heats of combustion, (3) assimilation 
