664 TRANSACTIONS OF SECTION M. 
factory character of the evidence adduced, proof that it is present in the living 
plant can never be proof that it has been formed in the up-grade process of 
assimilation, as there is reason to believe that it is a constant product of down- 
grade metabolism. However formed, its properties are such that it can never be 
present in more than minimal quantities; moreover, the fact that proof cannot 
be given that it is formed initially is of little consequence, as it is scarcely 
required, there being no other way apparently of accounting for the assimilation 
of carbon dioxide except the assumption that it is initially reduced to formic 
acid and then to formaldehyde. As to the manner in which carbonic acid under- 
goes reduction in plants, it is probable that water is ‘ electrolysed’ under the 
influence of light and chlorophyll, the one product being oxygen, which is 
evolved, perhaps, under the influence of a catalase, the other hydrogen, which 
is gripped temporarily by the chlorophyll and then used in reducing the carbonic 
acid. To assign a secondary part to chlorophyll and to regard iron salts as 
the primary agents, as Moore has done, is to overlook all that is known of the 
former substance and of the function of iron salts. 
To account for the formation of optically active dextroglucose in the plant, 
to take only one example, it is necessary to suppose that the polymerisation of 
formaldehyde is a directed process: probably it is formed against a sugar 
template, maybe under the influence of an enzyme. The enzymes, in fact, are 
to be regarded not only as hydrolysts but also as the primary formative agents 
of all directed metabolism. The manner in which they act reversibly may be well 
illustrated by reference to the behaviour of lipase. (Curves were exhibited 
showing the manner in which the synthetic and hydrolytic activities of lipase 
come to an equilibrium in presence of various amounts of water; it is most 
effective as a synthetic agent in the absence of water, a small proportion of 
water having a great effect in reducing the synthetic activity of the enzyme.’) 
The enzymes are rigidly selective agents. They appear all to be colloid 
materials, and therefore cannot be regarded from the same point of view as 
ordinary hydrolytic agents such as the acids; much confusion has been caused 
by the introduction of complex mathematical considerations in explanation of 
their action. Apparently they act at approximately linear rates, but as one or 
more of the products of change exert a retarding influence, the apparent rate of 
change is more nearly of a logarithmic order. 
Though starch is the first obvious product of assimilation, there is no reason 
to suppose that it is a necessary stage in the formation of the other carbohydrates 
met with in plants, as in monocotyledons and not a few other plants it only 
occurs in the guard cells and then only in minute amounts. Brown and Morris 
have, in fact, argued that cane sugar is the primary product of carbohydrate 
metabolism. A very thorough study of the problem is now being made at 
Rothamsted by Mr. Davis and others which promises to be of importance, 
especially as particular care is being taken to devise accurate methods of 
analysis. In no case has starch been found in mangold leaves except at a very 
early period, though cane sugar is always present together with invert sugar; 
apparently cane sugar wanders directly from the leaf into the bulb; maltose has 
never been detected, though specially looked for, so that it is probable that cane 
sugar is formed directly, not from maltose. 
Reference was made to the great importance to the agriculturist of exact 
methods of analysis and of knowledge based thereon of the composition of 
fodder crops: it was to be supposed that much could be done to improve the 
quality of the various crops if once the general character of their metabolism 
were established. Improvements in the methods recently effected at Rothamsted 
were then briefly described—particularly the method which Mr. Davis had 
introduced of estimating starch with the aid of Taka-diastase, whereby a mix- 
ture of maltose with glucose is produced instead of a mixture of maltose 
with dextrins of uncertain properties. To determine maltose with accuracy, 
Mr. Davis uses yeasts which were known to act selectively on this sugar 
- (Saccharomyces exiguus, S. Ludwigii, &c.). Incidentally, in the course of this 
work, the important fact has been established that yeasts which do not hydro- 
lyse maltose also cannot assimilate; the contrary results of previous workers 
1 Cf. Armstrong and Gosney, Proc. Roy Soc. Series B, 1914. 
