HOW EXPLAINED. 217 



ventilation, at this period, as will give the requisite degree of 

 dryness to the air within the house, is highly beneficial, 

 provided it be not increased to such an extent as to reduce the 

 temperature of the house much below the degree in which the 

 fruit had previously grown, and thus retard its progress to 

 maturity. The good effect of opening a Peach-house, by 

 taMng off the lights of its roof during the period of the last 

 swelling of the fruit, appears to have led many gardeners to 

 overrate greatly the beneficial influence, of a free current of air 

 upon ripening fruits ; for I have never found ventUation to 

 give the proper flavour or colour to a Peach, unless that frmt 

 was, at the same time, exposed to the sv/n without the intervention 

 of glass ; and the most excellent Peaches I have ever been able 

 to raise were obtained under circumstances where change of 

 air was as much as possible prevented, consistently with the 

 acl/rmssion of Ught {without glass), to a single tree." (Hort. 

 Trans., ii. 327.) 



This remark makes it evident that Mr. Knight used the 

 word ventilation in the sense of a draught or current of air ; 

 for it is dif&cult to conceive how plants can be more abundantly 

 supplied with fresh air than by removing the glass sashes 

 which obstructed its admission. 



It is not merely in heated houses or during the summer 

 season that free ventilation is required. It is just as necessary 

 in winter, or when plants are torpid. "We cannot suppose that 

 the substances contained within the living bark are at rest 

 during half the year, because the leaves have fallen away. On 

 the contrary, the change of colour which gradually takes place 

 in branches during winter, is proof enough that chemical action 

 is still going on in obedience to vital force. It is inconceivable 

 that such actions should be unconnected with the atmosphere 

 that surrounds the branches, although chemists may be unable 

 to explain the connection ; and without waitiag for the rationale, 

 we may assiu'e ourselves that those motions of the air which 

 are so indispensable in summer are at least as much needed in 

 winter ; perhaps more so. 



As to cold pits and cold greenhouses, they require that their 

 air should be kept in motion just as much as that of heated 



