The Plant. 89 



and succulent growth. The entrance of many comparatively in- 

 soluble compounds into the plant is made possible when they 

 assume a hydrated form, that is, when they are combined with 

 water. Silicon, for example, which forms comparatively insol- 

 uble soil compounds, is supposed to enter the plant as silicic acid, 

 which through dehydration or loss of water becomes deposited 

 as silica. Water is the chief constituent in green plants, its 

 amount varying from 80 per cent in grasses to 90 per cent in 

 root crops. Its amount decreases at the maturing stage. For 

 example, timothy grass, which contains on the average 80 per 

 cent of water, has when dead ripe 63 per cent of this constit- 

 uent. 



The importance of water in the transformation of carbohy- 

 drates will be shown in following paragraphs. It is important 

 to observe here that the constituents of water form 55.5 per cent 

 of starch and that their proportion is equally prominent in other 

 carbohydrates. Water bears similar importance in the structure 

 and transformations of all the other plant compounds. 



The carbohydrates form a widely distributed and prominent 

 group of compounds in the plant kingdom. They may be classed 

 in order of increasing complexity as follows: 



Mono-saccharides. 



Di-saccharides. 



Tri-saccharides. 



Poly-saccharides. 



Mono-saccharides are commonly represented by dextrose or 

 glucose, which occurs in most fruits. Artificial dextrose or " glu- 

 cose syrup ' ' is prepared commercially by the action of hot, dilute 

 sulphuric acid upon starch and subsequent removal of the acid 

 by means of lime. This is a hexose or six-carbon sugar, being 

 composed of six parts of carbon combined with the equivalent of 

 six parts of water. This structure, to which the name carbo- 

 hydrate (signifying carbon-water union) owes its origin, may be 

 confirmed by gently heating the sugar in a glass tube. Water 

 separates from the compound and collects on the adjacent cold 



