1907.] Photosynthesis of Carbon Dioade by Chlorophyll. 33 
thin. Secondly, except in the case of Composite the plastids of most white 
petals have faint but distinct traces of chlorophyll, either along the veins or 
in all parts. By Saxifraga Wallacei, Usher and Priestley presumably mean 
S. Campost Boiss, living petals of which plant are not procurable in 
Melbourne, but they would find it worth while to examine the petals for 
traces of chlorophyll or for a feeble power of independent photosynthesis in 
parts at least. That this explanation is the correct one is shown by the fact 
that the petals formed starch in a 0-001-per-cent. solution of formaldehyde 
when exposed to light, but not in darkness, whereas if the carbohydrate had 
been derived directly from the formaldehyde, without any photosynthesis of 
carbon dioxide, it should have been formed both in light and darkness. 
An equally strong objection applies to the experiment with Hlodea, which 
formed starch and gave off oxygen in a 0°02 solution of formic acid in light, 
but not in darkness, the explanation being that the formic acid decomposed 
and the carbon dioxide produced was assimilated. 
Hydroxyl and Peroxidase or “ Catalase” Enzymes. 
No conclusive proof has been brought forward to show that living plant 
cells even contain any appreciable amount of peroxide of hydrogen, and 
Pfeffer has conclusively shown in many cases, by the study of cells containing 
oxidisable pigments or chromogens, that no trace of hydroxyl is formed in 
them at any time. Russell* explains the action of plant tissues on 
photographic plates in the dark by assuming that they contain minute traces 
of hydroxyl, although it is not easy to see how this explanation could apply 
to a leaf which had been kept dried for 18 months to 3 years and still 
retained its power of affecting a photographic plate in darkness. There are 
many other possible explanations of the action, and hence by itself it affords 
no proof of the presence of hydroxyl. The oxidation of certain organic 
compounds yields hydrogen peroxide as a by-product, but in the living plant, 
as Loewt has shown, a catalase enzyme is generally present whose functions 
may possibly be to prevent the possibility of the accumulation of any 
hydroxyl, and the existence of such an enzyme was first noted by 
Schoenheinf. The presence of a “catalase” enzyme is, however, no proof 
that a plant contains or produces hydrogen peroxide, for ferments have been 
isolated from many plants to which they cannot be of any value (rennet and 
diastase ferments in fungi), or have a very doubtful one (peptic enzymes in 
latex). Usher and Priestley do not mention Loew’s work, and possibly were 
* © Roy. Soc. Proc.,’ B, vol. 78, p. 385. 
t Loew, ‘U.S. Dept. Agric. Report,’ 68, 1901. 
t ‘Journ. Prakt. Chem.,’ vol. 89, 1863. 
VOL. LXXX.—B. D 
