296 ON THE DEGENERATION 



Mrs. B. True; but plentiful irrigation is not always at- 

 tainable : where it can be had, no evil effects need be ap- 

 prehended from the sun. 



A deficiency of heat produces dropsy, and often rotting: 

 the most delicate parts of the plant first begin to decay, 

 such as the articulations of the branches and of the leaf- 

 stalks ; hence the leaves and young branches fall off. A 

 plant evaporates much more water than it retains ; it may 

 be compared to a tube into which you introduce water : 

 now, it is evident, that the more you pour in at one end, 

 the more must be poured out at the other : the evapora- 

 tion by the leaves must correspond with the absorption 

 by the roots, else the plant will suffer. 



Plants are also often injured by exposure to external 

 moisture. Rain is more hurtful to the wood than to the 

 bark ; the latter is a sort of great coat, provided by Na- 

 ture to shelter the wood from the inclemencies of the 

 weather : she has stored it with carbon, to enable it to re- 

 sist putrefaction ; and with siliceous earth, to render it 

 firm and durable : but if, as it sometimes happens, the 

 great coat be rent and ragged, the rains penetrates into 

 the wood (which is very differently organised,) and having 

 no means of escaping, the stem becomes rotten. 



Emily. Among the injuries plants sustain from rain, 

 we must not forget that of its making the pollen of flowers 

 burst before it is mature, and hence preventing the seed 

 from being brought to perfection. 



Mrs. B. True ; but we have already entered sufficient- 

 ly into detail on that subject. 



In regard to the influence of the air, I have formerly 

 observed, that the agitation which the wind gives to plants 

 is advantageous if not carried to excess : the cambium, 

 being a thick viscous juice, requires motion to promote 

 its descent. 



Caroline. Yet you have said, that the great aim of the 

 gardener is to retard the descent of the cambium, in order 

 that, by remaining longer stationary in the branches, it 

 may afford more nourishment to the fruit. 



Mrs. B. That is true, if the production of fruit be the 



1597. How is the result, if there is a deficiency of heatl 1598. . 

 What illustration is made with a tube of the absorption and evaporation 

 with plants! 1599. What is said of the injury to plants from rain! 

 1600. How does the air affect plants! 



