670 ‘REPORT—1899. 
starch production in the chlorophyll bodies could be induced by a large number of 
organic substances, including, amongst many others, asparagin, citric, tartaric, and 
lactic acids, leucine, tyrosine, and peptone. 
Very much more to the point are the experiments of Acton, made in 1889, and 
the still more recent work ot J. Laurent and of Mazé. 
In his experiments on terrestrial plants Acton, after depleting them of 
starch, immersed the cut branches or roots, as the case might be, in culture 
fluids containing certain organic substances, and took precautions to prevent any 
normal assimilation from taking place by depriving the air around the plant of any 
trace of carbon dioxide. He was not able to show the direct nutritive influence 
of so large a range of substances as Bokorny had done for Spirogyra, but his results 
leave no room for doubt that several of the carbohydrates, and even glycerine, can 
be absorbed by the roots, and can contribute to the nutrition of the green parts. 
Acton tried, amongst other substances, an ‘extract of natural humus, which was 
an aqueous solution of the extractives of a light soil which are soluble in dilute 
alcohol. This extract was found to be effective in producing a small quantity of 
starch in the leaves, and it evidently contained some substance or substances 
directly assimilable by the plant. 
Apparently without knowing anything of this work of Acton, J. Laurent has 
recently made a series of experiments on the culture of the maize plant in mineral 
solutions containing saccharose, glucose, or invert-sugar, and in this way has not only 
obtained, as Acton had done before him, evidence of the active formation of starch in 
the leaves, but has also found a very notable increase in the dry weight of the plant. 
Although assimilation of the carbohydrate may under these circumstances go on in 
darlmess, Laurent found that the process was much enhanced when light had 
access to the plant. Mazé, within the last few months, has obtained even more 
pronounced effects of this kind. 
When all these new facts are taken into consideration, I think they justify what 
{have already said, that we ought to demand more direct evidence than is at present - 
available before we accept the view that the majority of chlorophyllous plants 
take in the whole of their carbon from the atmosphere. In the cycle of change 
which the organic matter of the soil is constantly undergoing under the influence 
of micro-organisms, it seems by no means improbable that intermediate substances 
may be formed which in some measure directly contribute to the nutrition of the 
higher plants, and we must also by no means lose sight of the possible effect, in 
the same direction, of the symbiotic union of certain fungi with the root extremi- 
ties of many plants, the Mycorhize, whose functions are still so imperfectly 
understood. Then, again, we must remember that we have another possible 
extra-atmospheric source of carbon dioxide in the transpiration water of the plant, 
which is derived from a soil whose gases may contain 5 per cent. or more of carbon 
dioxide. From the amount of water transpired in a given time, and an application 
of the law of partial pressures, it may be readily shown that the supply of carbon 
dioxide to the aérial organs of a plant from this source is by no means negligible. 
Before these problems can be attacked for a particular plant with any hope of 
success, it is clear that we must have some means of establishing an accurate 
debtor and creditor account as between the plant and the surrounding atmosphere, 
and this account must extend over a sufficiently long period, and allow of an 
1 By far the most interesting and important result of Bokorny is the proof he 
gives that formaldehyde is directly assimilable by Spirogyra. His early attempts to 
show this had been rendered abortive by the highly poisonous nature of this sub- 
stance. The difficulty was surmounted by using a dilute solution of sodium oxy- 
methylsulphonate, which on warming with water splits up into formaldehyde and 
acid sodium sulphite, To prevent the unfavourable action of the acid sodium sul- 
phite, dipotassium or disodium phosphate was added to the plant cultures. In such 
a solution, with rigid exclusion of carbon dioxide, Spirogyra majuscula forms starch 
in its chlorophyll bodies, but the access of light appears to be necessary. 
- The importance of this experiment is very great in connection with Baeyer's 
well-known hypothesis that the first act of assimilation is the reduction of carbon 
dioxide and water to the state of formaldehyde. ; 
i i a 
