THE CARBOHYDRATES PRODUCED IN CROPS 127 



and used for rougher material. The crude material, on 

 arriving in this country, has to undergo a certain amount 

 of treatment through sub-divisions by a process of combing. 

 Jute fibre is a very crude type of cellulose, or, more strictly, 

 ligno-cellulose, and usually contains about 10 per cent, water 

 and 30 per cent, matter soluble in acids and alkalies. 



Hemp. Hemp is used chiefly for the production of 

 rope, and is a very crude form of cellulose. Many different 

 plants are used for the production of hemp, but the chief 

 hemp-producing plant, Cannabis sativa, grows about nine 

 feet high, and is treated like flax. 



Timber. A very crude and imperfect form of cellulose 

 constitutes the main structure of all kinds of timber. The 

 growth of timber trees constitutes the whole science of 

 forestry, a very large subject indeed. The hard woods, 

 like oak and beech, grow slowly, whilst some of the coniferous 

 trees, such as Japanese larch, grow to a usable size in twenty- 

 five or thirty years. Timber is only economic on very inferior 

 land or remote situations. Trees are generally felled in the 

 middle of the summer or winter, to avoid felling them at 

 the time when the sap is moving. After felling, the logs 

 are sawn up into planks. 



About 1660 a great move was made in planting timber, 

 and in 1776 Dr. A. Hunter was able to tell the Royal 

 Society "there is reason to believe that many of the ships 

 which, in the last war, gave laws to the whole world, were 

 constructed from oaks planted at that time " (i.e. 1660 

 and thereabouts). To-day it is our Army rather than our 

 Navy that is so dependent on home-grown timber, but we 

 cannot congratulate ourselves on the wisdom of our fathers 

 as Dr. Hunter did in 1776. The resuscitation of home-grown 

 timber production has happened before, and it must happen 

 again. 



Seasoning timber is necessary to prevent warping after 

 use. Some form of preservative of timber for building 

 purposes is often needed. Of these, creosote stands in the 

 front rank, and a preparation called Burnett's Fluid, or 

 strong zinc chloride solution (about 50 per cent.), is also used. 



