70 PLANT LIFE 
and diffusible sugar, travels in the latter form 
to other parts of the plant. It passes to the 
growing regions, where it is utilised in growth 
processes, to storage tissues where it is re- 
converted into starch or into some other food 
reserve, or it is drawn towards any other centre 
of activity where a consumption of carbo- 
hydrate is in progress. 
We have learned in a former chapter that 
water plays an important part in _ photo- 
synthetic production of carbohydrate. It 
not only acts as a physical agent, by main- 
taining the protoplasm in that state of watery 
consistence essential to chemical change, but 
it also forms part of the raw material which 
enters into the actual composition of the 
sugars and similar substances. Furthermore it 
serves as the vehicle by which salts containing 
phosphorus, sulphur and other substances 
which enter into the composition of proto- 
plasm, or are essential to its proper working, 
can enter the plant from without. The excess 
of water is eliminated from the plant by the 
diffusion or transpiration of the watery vapour 
through the stomata. 
