95 



and acetylene, still more are volatile liquids, a mixture of these 

 being the petrol of the motorist, others again are oily, others 

 jelly-like, yet others hard and waxy. On the chemical side they 

 may be grouped into series each containing many members having 

 a general resemblance in the internal structure of their molecules 

 and their chemical behaviour. As examples of such series may be 

 mentioned the paraffin, olefine, benzene, napthalene and anthracene 

 series. Many hydrocarbons occur in nature ready formed in 

 mineral oils and waxes and in the volatile oils of plants, others are 

 obtained by destructive distillation of coal and other organic sub- 

 stances, yet others have been built up by synthetic methods. The 

 number of hydrocarbons is very great, but that of compounds 

 derived from or connected with them is far greater, but, important 

 and interesting as is the subject, I cannot now pursue it farther. 

 Of many classes of carbon compounds I must omit even a bare 

 mention, but I will just give the names of two or three such 

 classes. The metallic carbides are the compounds of carbon and 

 metals, those of calcium, aluminium and iron being of special 

 interest. 



Carbohydrates contain carbon, hydrogen and oxygen, the 

 two latter elements in the same proportions as in water. This 

 class include the starches, dextrins and sugars. Compounds of 

 still greater complexity, containing nitrogen as well as the three 

 elements just mentioned, are characteristic of all living organisms 

 whether animal or vegetable. In this planet, at least, carbon 

 compounds are the indispensable vehicle for the manifestation of 

 life. 



My time is now exhausted. I aimed, in this lecture, at giving 

 such an account of the chemistry and physics of carbon and its 

 compounds as should help those who have not studied chemistry 

 or have forgotten what they once knew to follow intelligently the 

 remaining lectures of the series. I could not expect completely to 

 attain my aim, but I hope that I have not altogether missed it. 



Note. — This lecture was illustrated by a number of experi- 

 ments. 



II. 



The Uses of Carbon in Plants. 



By Rev. Professoe G. Henslow, M.A., F.L.S., Etc. 



(Read before the Botanical Section, February 24th, 1916.) 



/^ARBON (C), in combination with the elements of water (H s O), 

 ^ forms the entire structure or framework of plants chiefly as 

 a substance called Cellulose (C 6 Hio05) and its various modifica- 

 tions according to the locality in the plant. 



In the mineral condition carbon is only pure in the diamond ; 



