II] LEAVES AND RIPENING 35 



without their proper sweetness because of the cutting- 

 off of the supply of sugar. Stopping the growing points 

 of the plant is justifiable, because thereby the material 

 manufactured together with whatever may be in reserve 

 in the stems or roots will be thrown wholly into the fruit 

 and is not wasted in making unnecessary new growth ; 

 but to the final heaping up of sugar and similar sub- 

 stances in the fruit the continued action of the leaf is 

 indispensable. In the case of grapes, it has been shown 

 that to cut off any large proportion of the leaves with 

 the idea of more completely exposing the grapes to the 

 sun reduces not only the size of the grapes, but their 

 richness in sugar as well. What ripening action is 

 caused by the direct rays of the sun is not known, but 

 probably the increased warmth they cause induces in 

 apples and pears a quicker change of starch and similar 

 materials into the sugar and aromatic bodies which mark 

 the ripe fruit. The sunny side of the fruit is never, 

 however, very much ahead of the shaded side, so that we 

 may conclude that the shading is not of much moment 

 in delaying ripening, whereas the absence of leaves has 

 a seriously detrimental effect. 



Assimilation and respiration donot,however,represent 

 the whole of the work of the leaf; it has one other 

 fundamental piece of work to do, that is, to get rid of 

 water from the plant. We can illustrate this action by 

 several simple experiments ; for the first, take a test-tube 

 with a well-fitting soft cork, and slit the cork in two down 

 its length. Then introduce a long thin leaf (a barley or 

 a daffodil leaf will do, according, to the time of year) into 

 the tube, and cork up the tube with the leaf between the 

 two halves of the cork. Leave the tube thus hanging on 

 to the plant until the next day, when a plentiful deposit 

 of water will be found inside the tube. For a second 

 experiment, take a pot containing some actively growing 



