TRANSACTIONS OF SECTION B. 629 



have been discovered, and pure chemistry will then be practically exhausted, and 

 "vrill be in the same condition as systematic botany and mineralogy now are. 

 New compounds will now and then be discovered, just as new plants and new 

 minerals now are, but nothing further will be brought to light that will afiect 

 the theories at which we shall then have arrived, whatever they may be. AJl 

 the material with which the science has to deal having then been brought together, 

 what will happen ? Will chemical science cease ? Will chemists, satisfied with 

 past achievements, cease to work, confining themselves to practical questions and 

 the history of the days gone hj? I think not. The scieoce will continue to 

 develop, but it will be in other directions than those previously pursued. The 

 exhaustion of systematic botany has not put an end to botanical science, for 

 vegetable physiology has opened a wide field to the botanist, one that will take a 

 long time to explore thoroughly. To indicate the directions which chemical science 

 will take in its various applications to other departments of knowledge, as, for 

 instance, in connection with the study of the physical properties of matter, or in 

 elucidation of the chemical processes whereby minerals have been formed, or those 

 through which geological strata have passed in bygone ages, would not be within 

 my competency, as I should have to touch on subjects with which I am not familiar ; 

 but I may be permitted to refer in a few words to a subject, with which, by reading 

 at least, I have become better acquainted, and which seems to me to ofler a wide 

 field to the investigator who shall come well provided with physical and chemical 

 knowledge to its cultivation. I allude to the processes whereby the substances 

 constituting the various organs of plants and their contents are formed, and those 

 again to which the decomposition and decay of vegetable matter are due ; a subject 

 as to which our knowledge is quite elementary, but which, it seems to me, admits 

 of an extension and development of which we have at present not the least con- 

 ception. 



De Saussurc, it is well known, first discovered the fact that plants under the 

 influence of light absorb carbonic acid and give off oxygen, the inference of course 

 being that the carbonic acid and the water present are decomposed, the carbon of 

 the former and the hydrogen of the latter going to form the various organic con- 

 stituents of the plant, while the oxygen or a part of it is set at liberty and poured 

 into the atmosphere. The facts as they stand are simply these : what the plant 

 requires for its subsistence is carbonic acid, water, nitrogen in some form (presum- 

 ably that of a nitrate), certain bases — potash, lime, magnesia, iron oxide, and 

 phosphoric acid. Out of these it constructs the whole of its organic frame, its cells 

 and their contents, re-arranging the elements of which its food consists in such a 

 manner as to convert inorganic into organic matter, i.e. changing bodies in which 

 the affinities of the atoms are thoroughly satisfied into such as contain them in a 

 state of more or less unstable equilibrium, and therefore liable to alteration when 

 their atoms are allowed to act in accordance with their natural affinities. More 

 than this we do not know ; our ignorance of tlie several steps or stages of the pro- 

 cess, if there are any such steps, is complete ; all that has been added to the general 

 statement just given is mere speculation. Yet it is impossible to remain 

 satisfied wdth the present state of our knowledge on the subject. Accordingly 

 numerous attempts have been made to bridge over the chasm which separates the 

 inorganic and organic worlds, not indeed to show that the change does not involve 

 the creation, as was once supposed, of new matter — for this was proved lono' a^o — 

 but to exhibit in its details the hidden mechanism which produces it — but hitherto 

 without success. We kuow that light is essential to the process of assimilation in 

 plants, since the process does not go on in the dark ; but this fact does not help us to 

 an explanation, for light in this case is a mere stimulant, and never produces the same 

 or similar effects outside the vegetable organism. Liebig and others have attempted 

 to show that the process of assimilation in plants commences with the formation of 

 some simply constituted body, such as oxalic or formic acid, with the elimination 

 of oxygen, out of which by condensation and further separation of oxygen more 

 complex bodies, such as sugar, fats, &c., are formed ; but there is not the slightest 

 evidence at present in favour of this view. The first product of assimilation that is 

 distinctly recognised is starch, a highly complex organic, one might almost say an 



