TRANSACTIONS OF SECTION K. 7S7 



line of research, I do not wish to miuimise the difficulties that accompany it. 

 Difficulties of method assume considerable magnitude, for we have here no question 

 of section cutting and microscopic examination. Vegetable pli3'siology is allied very 

 closely to other sciences, aud research into its mysteries involves more than a 

 preliminary acquaintance with them. Especially must one point out the im- 

 portance, indeed the necessity, of acquaintance with a certain range of organic 

 chemistry and with cliemical methods of work. In certain directions, too, physics 

 are as much involved as chemistry in others. The bearing of these sciences in 

 particular directions will be referred to later. 



I fear another obstacle stands at the threshold of research which looks suf- 

 ficiently formidable. The so-called fundamental facts of vegetable physioloo-y 

 have been laid down with sufficient dogmatism in text-books by many writers 

 whose names carry with them such weight that it appears almost heresy to question 

 their statements. We have been content to accept many things on the authority 

 of the great workers of the past, with the result that the advance of knowledge 

 hcii been hindered by such acceptance of what were deemed facts, but were 

 really inaccuracies. We may refer, for instance, to the statement made by Boussin- 

 gault, and accepted by most botanists ever since his time, that the absor})tion of 

 carbon dioxide from the air takes place by means of solution in the cuticle of the 

 epidermal cells of plants and thence passes by diffusion to the seats of photosynthesis. 

 Only comparatively recently has this been shown to be erroneous. If, however 

 it is once recognised that authority is fallible this apparent obstacle becomes the 

 opposite. The more evident questions have not yet been solved, leaving only 

 the more difficult ones for the present-day worker. 



Recognising the importance of work in this field, and realising that with the 

 advent of a new century new departures must be taken, I have thought I mi"-ht 

 \^^nture to direct the thoughts of my hearers, many of whom I may call my 

 colleagues, to the present position of certain problems which have long been the 

 subjects of speculation and which offijr the prospect, if not of complete solution, at 

 aay rate of considerable advance if investigated by modern methods. 



I turn first to a few questions connected with the nutritive problems of plants 

 in general. 



There are several theories abroad as to the progress of events during photo- 

 synthesis, none of which can be regarded as entirely satisfactory. For many 

 reasons it seems desirable that this question shall be thoroughly investigated in 

 the light of the present condition of both chemical and physical science. I may 

 perhaps venture to recall to you the principal hypotheses of carbohydrate forma- 

 tion which have been advanced, so that its present position may be properly 

 appreciated. 



The view that has met with the widest acceptance is that of Baeyer. On his 

 hypothesis the carbon dioxide absorbed is decomposed under normal conditions to 

 y^eld carbon monoxide and oxygen ; a corresponding and coincident decomposition 

 of water leads to the production of free hydrogen and oxygen. The oxyn-en from 

 both sources is exhaled, while the carbon monoxide and hydrogen combine to form 

 formaldehyde. The formaldehyde gives rise by a process of polymerisation to 

 some form of sugar. 



A. modification of this hypothesis has been advanced, which suggests that the 

 preliminary decomposition of the carbon dioxide and the water may not take 

 place, but that by a rather less violent reaction between them the formaldehyde 

 may be formed and the oxygen liberated. 



Erlenmeyer has suggested a somewhat different course of reaction, yielding 

 substantially the same results. He thinks it possible that the first interaction of 

 carbon dioxide and water leads to the formation of formic acid and hydroo-en 

 peroxide, and that these subsequently interact with each other, yielding form- 

 aldehyde and water and giving off oxygen. ° 



Many years after the views of Baeyer appeared, a hypothesis of a different 

 nature was proposed by Crato. He suggests that the carbon dioxide after 

 absorption becomes ortho-carbonic acid, and that this remains in solution in the 

 cell sap. This acid has the structure of a closed benzene ring in which six 



3 G 2 



