XXVI INTRODUCTION. 



them is attended with success for a similar reason. 

 Wherever the roots are cut through, the new fibres 

 which are emitted, provided a plant is in health, in short 

 tufts, and each terminated by a spongiole, are much 

 more easily taken out of the ground without injury than 

 if they were longer and more scattered among the soil. 

 When destroyed, the spongioles are often speedily re- 

 placed, particularly in orchard trees, provided a slight 

 degree of growth continues to be maintained. This is 

 one of the reasons why trees removed in October succeed 

 better than if transplanted at any other time. The growth 

 of a tree at that season is not quite over ; and the first 

 impulse of nature, when the tree finds itself in a new 

 situation, is to create new mouths by which to feed when 

 the season for growing again returns. 



Evaporation takes place in plants to an inconceivable 

 degree in certain circumstances. It is known by the 

 experiments of Dr. Hales, that a sunflower plant will 

 lose as much as lib. 14 oz. by perspiration in twelve 

 hours ; and that in general, " in equal surfaces and 

 equal times, a man would perspire sV, the plant T <br, or 

 as 50 : 15 ; " and that taking all things into account, a 

 sunflower perspires 17 times more than a man. The 

 same most accurate observer found that a cabbage per- 

 spired in twelve hours 1 Ib. 9 oz. ; a Paradise Stock in a 

 pot, 11 ounces ; and a Lemon Plant, 8oz. Guettard 

 states that he found Cornus Mascula perspire twice its 

 own weight in a day ; and Mr. Knight has remarked 

 a Vine in a hot day losing moisture with such rapidity 

 that a glass placed under one of its leaves was speedily 

 covered with dew, and in half an hour the perspiration 

 was running off the glass. In damp or wet weather 

 this evaporation is least ; in hot dry weather it is great- 

 est. This loss has all to be supplied by the moisture 

 introduced into the system by the spongioles ; and 

 hence, if the spongioles are destroyed, and evaporation 



