216 ON THE HEAT IN FORCING-HOUSES. 



and subsequently kept cool by the evaporation of the water during the 

 night : in the other, the steam is precipitated upon the leaves and 

 branches of the trees, to which it necessarily communicates much heat. 

 The former operation nearly resembles that of the shower-bath, some- 

 times used in this country, in which the patient is suddenly chilled by a 

 heavy shower of cold water ; the other resembles the hot steam-bath of 

 Russia, in which he is violently heated ; and if the gardener were to try 

 each of these processes upon himself, during a single night, I suspect he 

 would arise in the following morning with very different feelings, unless 

 he were blest with much peculiar hardness of constitution. It is true, 

 that plants do not appear to possess sensation in the ordinary sense of 

 that term, as it is applied to animals ; but nature, in forming its whole 

 organic creation, seems to have proceeded so much by substitutions and 

 additions, that simple sensation, in its strict and limited sense, abstracted 

 from all powers of perception, may not improbably be as widely diffused 

 as organisation itself; and animal and vegetable life may be, in conse- 

 quence, susceptible of similar injuries from similar external causes. The 

 influence of hot and damp air upon both, is greatly more powerful 

 than that of dry air of the same temperature. In the experiments of 

 which Sir Charles Blagden has given an account in the Philosophical 

 Transactions of 1775, he, with Sir Joseph Banks and others, sustained 

 without injury a temperature of 260 degrees in dry air ; but they found 

 damp air, at half that temperature, to be scarcely supportable : and 

 every gardener knows, how quickly the leaves of his plants are injured 

 by the combined action of heat and moisture. 



The succulent shoots of trees, however, always appear to grow most 

 rapidly, in a damp heat, during the night ; but it is rather elongation 

 than growth which then takes place. The spaces between the bases of 

 the leaves become longer, but no new organs are added ; and the tree, 

 under such circumstances, may with much more reason be said to be 

 drawn, than to grow ; for the same quantity only of material is extended 

 to a greater length, as in the elongation of a wire. 



Another ill effect of high temperature during the night is, that it 

 exhausts the excitability of the tree much more rapidly than it promotes 

 the growth, or accelerates the maturity of the fruit : which is in conse- 

 quence ill supplied with nutriment, at the period of its ripening, when 

 most nutriment is probably wanted. The muscat of Alexandria, and 

 other late grapes, are, owing to this cause, often seen to wither upon 

 the branch in a very imperfect state of maturity ; and the want of 

 richness and flavour in other forced fruits is, 1 am very confident, often 



