10 GROWTH OF PLANTS. 



grow as much as a foot in one day,, and twenty-two 

 feet and a half in eighty-seven days. 



When the new layer of wood begins to harden, the 

 rise of the sap is checked, and towards the end of 

 autumn, little or no sap rises, while all the pulp and 

 the watery vapour imhibed from the atmosphere 

 descends. The vessels of the leaves consequently not 

 being supplied with fresh pulp, are emptied and shrink, 

 an effect sometimes hastened by the pressure of the 

 newly-formed bud ; and the leaves become detached 

 and fall, except where the juices are very thick, as in 

 holly, or resinous, as in fir, when the leaves do not 

 fall till the new wood is formed. That the fall of the 

 leaf is not caused by cold, is proved by the early fall 

 of those of the ash or poplar ; or by withering, appears 

 from their adhering firmly to a branch cut off or killed 

 in summer. 



In India, where almost all trees, even our oaks, are 

 evergreen, they produce an artificial fall of the leaf by 

 uncovering the roots during the violent heats, for the 

 purposes of subsequent forcing. When gardeners 

 observe in their cuttings that the leaves wither and 

 remain, they consider ^that the plant will not strike; 

 but when the leaves fall, success is more certain, as 

 this indicates that the swelling of the bud at the base 

 has cut off the supply of sap. 



AGE OF PLANTS. 



SOME plants, such as the minute funguses, termed 

 moulds, only live a few hours, or at most a few days. 



