86 



Plant Physiology 



On a large scale, a rapid loss of water from plants is 

 familiar to all in the process of hay-making. The differ- 

 ence in weight between green and dry hay is perfectly 

 obvious. There may, of course, be a slight loss of water 

 from the cut surfaces of the stems, but even should these 

 be sealed by paraffin or wax, wilting and loss of water will 

 proceed almost as rapidly as before. Practically all parts 



FIG. 24. Potometer with shoot-chamber (A), small-bore record-tube 

 (B), water-reservoir (C), and stop-cock for refilling tube (>), sup- 

 ported by base (E). [Adapted from Ganong.] 



of plants lose water to at least a slight extent. Apples or 

 potatoes stored in a fairly dry situation during a consider- 

 able period of time will show considerable loss, although 

 the normal surfaces of such parts are so constructed that 

 rapid drying-out is prevented. 



As soon as wilting takes place, sufficient practically 

 to close the stomata, the rate of loss will drop, and thus 



