Pioneer Investigators of Photosynthesis. 203 
the oxygen of the air. On the contrary, they change it into 
carbonic acid gas which may be found in small quantities stored or 
dissolved in the succulent tissues just as it would be in pure water ; 
otherwise they do not alter it. The carbonic acid which the non¬ 
green parts form with the surrounding oxygen traverses the plant, 
ultimately to be decomposed in the leaves. Leaves of marshy 
plants, succulents and evergreens grown under otherwise similar 
conditions use less oxygen than do the leaves of other plants.” 
In his sixth chapter, section 3, he expresses surprise that in no 
case could plants decompose carbon monoxide. That plants could 
utilise this gas has been asserted and denied again and again, e.g., 
by Stutzer, Just and others. Even as late as 1903, Bottomley and 
Jackson brought forward fresh evidence of the nutritive value of 
carbon monoxide, given certain conditions. 
The seventh chapter of his book deals with the decomposition 
and fixation of water by plants, which De Saussure says takes 
place coincidently with the fixation of carbon :—“ Plants appropriate 
the elements hydrogen and oxygen from water, and in doing so 
cause it to lose its liquid state, but this assimilation is not very 
pronounced unless carbon be appropriated at the same time. 
Water fixed or incorporated by plants can apparently only lose its 
oxygen in the form of gas after the death of the plant or of one of 
its parts. As soon as plants which have assimilated the oxygen and 
hydrogen of water begin to ferment without contact with free 
oxygen, they then form carbonic acid exclusively from their own 
tissues. The oxygen of the combined water can then unitewith carbon 
to form carbonic acid gas, and the plants or growing organs in 
dissociating oxygen from this carbonic acid eliminate indirectly an 
element originally belonging to the water. Thus by the combined 
action of vegetation and fermentation operating without contact 
with air, water can give off its chief element in the form of oxygen. 
In no case, however, do plants directly decompose water in assimi¬ 
lating hydrogen and in eliminating oxygen as a gas. They never 
exhale oxygen save as a consequence of the direct decomposition of 
carbonic acid. Thin-leaved plants growing in pure water in an 
atmosphere of oxygen and nitrogen—and subjected to the successive 
influence of light and darkness do not exhale oxygen and give no 
external indication of the direct decomposition of water. It is 
impossible to attribute to the direct decomposition of water the 
oxygen which they emit into an atmosphere of nitrogen, or under 
water, because whenever oxygen is lacking from their environment 
