NUTRITION. 85 



once upon digestion, and is termed watery exhalation. 

 According to Miquel and Decandolle, heat has a sen- 

 sible action upon the increase of the former, whilst 

 within certain limits it has very little upon the latter. 



59. The loss of water by the plant from exhalation 

 at the leaves, is accompanied also by the absorption at 

 the same place of fresh quantities generally exceeding 

 in amount the former, though the reverse in some cases 

 may hold good. 



60. In a general way we may say that plants with 

 tender leaves transpire more than those of a firm and 

 coriaceous texture, and that in Evergreens the exhala- 

 tion is but very little in comparison with other plants ; 

 and Hales calculated that fleshy fruits transpire the 

 same quantity that leaves do in relation to the extent 

 of exhaling surface. 



61. Circulation. We have now to speak of a very 

 complex subject connected with the nutrition of plants, 

 and regarding which at the present moment it is diffi- 

 cult to arrive at a definite conclusion. This subject is 

 the motion of elaborated fluid through different parts 

 of the plant, and which in some of its relationships is 

 held to be analogous to the circulation of the blood in 

 animals . 



62. In the observations which follow, the views of 

 Meyen, of Berlin, upon this point, are those which are 

 regarded, and which will be found fully developed in 

 the 2nd Vol. of his System of Physiology, the nature of 

 this work forbidding all lengthened and controversial 

 points being entered into. 



63. In 1772, an Abbot and Professor of Physic at 

 Reggio, Corti, discovered a motion of fluid taking place 

 in the cells of certain plants called Charas, since which 

 time up to the present period numerous observations have 

 been made upon these and other plants in which nearly 

 a similar motion has been seen to take place. 



64. The Charas are plants situated low down in the 

 scale of vegetable bodies, being more nearly allied to the 

 Conferoe than to any others perhaps, but forming a 



