////•. ruYsioi.oay 01- I'I.axts 285 



ccnistructivL' work of the plant. The water is not 

 all wanted ; part of it jxisses off in the form of 

 vapour. Transpiration, then, is the ]:)assin<^ off 

 of this water. 



We can easil)- see this process L^oing on if we 

 place a few trop;eoluin leaves in a cool tumbler, 

 and then expo.se the tumbler to sunlight. In a 

 .short time the sides of the i;la.ss will .show a film 

 of moisture due to the transpiration (jf the leaves. 

 This process takes place more freel}' in a warm 

 temperature than in cool conditions ; consequentl\^ 

 in hot weather there is rapid trans[)iration, and as 

 the water is parted with more cell sap passes into 

 the leaves and stems, and so the plant is kept cool. 

 We can now see the i^reat use of the little pores 

 known as Stoniatcs ; these arc found mainly on 

 the under surface, and it is princi{)ally through 

 these [)ores that the leaf transpires. 



We must now carefully note the fact that all 

 growing parts of the plant take up ox}'gen and 

 give off carbon-dioxide. This power which is 

 common to all life is known as respiration. It 

 is a process that cannot be observed in daylight 

 in green plants because this respiration is feeble, 



