32 Dr. A. J. Ewart. Supposed Extracellular [Oct. 11, 
The chloroplastids in the cells, after exposure and testing, show mostly a 
strong violet tinge when examined, but a slight tinge can usually be distin- 
guished in the protoplasm, so that apparently the formaldehyde diffuses 
somewhat from the chloroplastids to the protoplasm, and, further, is not 
formed in all the chloroplastids even of one and the same cell. Furthermore, 
precisely the same production of “formaldehyde” is shown when the green 
tissues are exposed to light in an atmosphere free from carbon dioxide. It 
might be suggested that possibly a post-mortem production of carbon dioxide 
took place. Accordingly, leaves of Vallisneria, Hlodea, and grasses killed by 
chloroform, ether, and heat were enclosed in vessels on clean strips of glass 
and kept in darkness for two and for 12 hours. The vessel contained a 
solution of caustic soda, and half of the inner wall was lined by a sheet of 
asbestos soaked in caustic soda. On then exposing to light until the leaves 
were nearly or completely bleached, all of them without exception developed 
a pink coloration with decolorised magenta, and the colour was as strong 
as that developed in the presence of carbon dioxide. In similar fresh leaves no 
formaldehyde whatever could be detected. It is evident, therefore, that Usher 
and Priestley have misinterpreted the facts, and that chlorophyll, when exposed 
to light in the presence or absence of carbon dioxide, yields an aldehyde, 
presumably formaldehyde, merely as a decomposition product. Interesting 
and suggestive as this fact may be, it affords no proof that formaldehyde is 
a product of photosynthesis, or that the latter can take place outside the 
living cell. The idea has more than once been put forward that chlorophyll 
itself is a product of photosynthesis, and that carbohydrates are formed by 
molecular changes and rearrangements in it taking place under the action and 
with the aid of light energy. 
On examining parts of leaves growing in nature, but which had become 
bleached or discoloured, traces of formaldehyde appeared to be present in 
many cases, whether examined in the early morning or evening, and pre- 
sumably in these cases also the aldehyde results from the decomposition of 
the chlorophyll. | 
Usher and Priestley state that on floating the white petals of Saxi/raga 
Wallacei on water in the presence of carbon dioxide and sunlight, and after 
painting the petals with chlorophyll, the plastids in the cells developed starch 
grains, and they consider this to prove an extracellular decomposition of 
carbon dioxide outside the petals. In any case it would only prove that the 
traces of formaldehyde produced by the decomposition of the chlorophyll can 
be synthesised by the plastids to carbohydrate, and the experiment is open to 
two very serious objections. Firstly, the petals are cuticularised, and formal- 
dehyde diffuses only very slowly through cuticle, even when comparatively 
