216 KNIGHT'S OBJECTION TO VENTILATION. 



pole formed a radius ; but in no other direction. Thus ciroumstanoed, 

 the diameter of the tree from north to south in that part of its stem 

 which was most exercised by the wind, exceeded that in the opposite 

 direction, in the following autumn, in the proportion of thirteen to 

 eleven." 



Now, if the efiFect of motion is to increase the quantity of wood in a 

 plant, it is eyident that ventilation, which causes motion, must tend to 

 produce a healthy action in the plants exposed to it ; and such a state 

 must also be favourable to the development of all those secretions upon 

 which the organisation of flowers, the setting of fruit, and the 

 elaboration of colour, odour, flavour, &o., so much depend. Some 

 suggestions by Mr. Knight, as to the manner in which this result can 

 be artificially produced, wiU be found in the Sort. Trans., vol. iv. 

 p. 2, and 3. (See also Hort. Trans,, new series, i. 34.) 



It is not a little remarkable, however, that the same great 

 gardener as weU as physiologist should have expressed himself 

 unfavourable to abundant ventUation. It would seem as if he 

 scarcely perceived the whole b^g,ring of the interesting 

 experiment just recorded. It may be objected, he says, that 

 plants do not thrive, that the skins of Grapes are thick, and 

 other fruits without flavour, in crowded forciug-houses : but in 

 these it is probably Hght, rather than a more rapid change of 

 air, that is wanting ; for, in a forcing-house which I have long 

 devoted almost exclusively to experiments, I employ very little 

 fire heat, and never give air till my Grapes are nearly ripe, iu 

 the hottest and brightest weather, further than is just necessary 

 to prevent the leaves being destroyed by excess of heat. Yet 

 this mode of treatment does not at all lessen the flavour of the 

 fruit, nor render the skins of the Grapes thick ; on the contrary, 

 their skins are always most remarkably thin, and very similar to 

 those of Grapes which have ripened in the open air. {Hort. 

 Trans., ii. 235.) 



Mr. Knight would not even admit that in forciug-houses 

 ventilation is useful at the period of ripening ; but the following 

 extract, in which this opinion is expressed, shows that he did 

 not use the word ventilation in its ordinary sense. " A less 

 humid atmosphere is more advantageous to fruits of all kinds, 

 when the period of their maturity approaches, than in the 

 earlier stages of their growth ; and such an increase of 



