1907.| Photosynthesis of Carbon Dioxide by Chlorophyll. 35 
to any previous worker with this method. This fact takes away all decisive 
value from the negative observations of Kny* and of Czapekt in regard to 
the absence of any power of evolving oxygen from isolated droplets of 
chlorophyll or from droplets imbedded in foreign protoplasm when tested by 
the bacterium method. The bacterium method must, therefore, be applied 
with great caution to chlorophyllous cells which have been exposed to strong 
light when in an abnormal, depressed, or dying condition. The only 
observations which seem to support those of Usher and Priestley, and show 
that an evolution of oxygen is possible when chlorophyll is exposed to 
sunlight apart from living protoplasm, are those of Molisch,t who found by 
the aid of luminous bacteria that chloroplastids from dried dead cells were 
able to evolve oxygen. Since, however, Molisch with the same means was 
unable under any circumstances to detect any evolution of oxygen from 
healthy cells rich in etiolin, but free from chlorophyll, it is evident that this 
method of Beyerinck’s is not always reliable. The fact that chloroplastids 
may remain capable of photosynthesis outside the cell says nothing, for they 
do not retain this power long, whether kept in light or darkness, and have 
a photoplasmic basis. Nevertheless, it is quite possible that some of the 
cases of partial or complete assimilatory inhibition} observed by me may 
result from an interference with the later processes of polymerisation, such 
interference rapidly reacting on the primary stages of photosynthesis. This 
is very probably the case when the accumulation of the products of 
photosynthesis increasingly retards further production. Photosynthesis is, 
however, certainly not the simple physico-chemical process that Usher and 
Priestley imagine it to be, but involves vital activity and control in all 
its stages. 
It is, in fact, difficult to see how a simultaneous production of formaldehyde 
and hydroxyl could be possible in films exposed to sunlight, for as Geisoull 
has shown, hydroxyl reacts with neutral or acid solutions of formaldehyde, 
forming carbon dioxide, water, and hydrogen. This reaction is only shown 
in a test-tube on warming, but if a Vallisneria leaf which has accumulated 
formaldehyde is soaked in hydroxyl and exposed to strong sunlight or 
warmed, the formaldehyde disappears. Boiling with hydroxyl does not, 
however, remove from gelatine its power of producing a pink colour 
with decolorised magenta. Hence its “aldehyde” constituent is not 
formaldehyde, a fact which Dr. Rothero has confirmed by distillation tests. 
* Kny, ‘ Ber. d. Bot. Ges.,’ 1897, vol. 15, p. 388. 
+ Czapek, ‘Ber. d. Bot. Ges.,’ 1902, vol. 20, p. (44). 
t ‘Bot. Zeit.,’ 1904, vol. 62, I, p. 1. 
§ ‘Linn. Soc. Journ.,’ 1896, vol. 31, pp. 429, 367. 
|| ‘Ber. d. D. Chem. Ges.,’ 1904, vol. 37, p. 515. 
