UPON PLANT-HOUSES. 97 



impedes the full development of its trees, so does the same 

 happen in a crowded house. Hence the area must be propor- 

 tionate to the production of branches and leaves. That those 

 structures are in many cases overloaded with plants, is proved 

 by the practice of removing many of these out of doors, into the 

 open air, in summer; the remnant being mostly numerous 

 enough to occupy the entire space, without preventing commo- 

 dious access. 



9. The more spacious the building is, the greater opportunity 

 does it afford for cultivating also plants which thrive under con- 

 siderable privation of light ; that is to say, such of these as are 

 kept irrespectively of their flowering, or which may be accom' 

 modated with light at that particular period, or else are accustomed 

 to blossom in the shade. 



10. The organisation of trees fits them, in a greater degree 

 than plants of lower stature, to have the loss of light compensated 

 by an increase of temperature in the soil ; and they demand, 

 accordingly, especial care in that respect, during the season of the 

 year, when the scanty supply of light indicates a judicious and 

 cautious increase of bottom -heat in the building. 



1 1. Since the forest- vegetation is, on the whole, more dependent 

 on periodical light than the ground- vegetation (Flurvegetation), it 

 follows that we must em ploy a variety and complication of appliances, 

 in order to modify the effect of light and shade, which are less 

 indispensable in the low houses (propagating stoves) where her- 

 baceous and the like plants are chiefly and extensively cultivated. 



1'2. These last-mentioned buildings and plants ought to have 

 as much as possible continuous daylight, in conformity to what 

 takes place in their natural place of gi'owth ; whereas 



13. The lower forest- vegetation demands a strong degree of 

 direct light, and if equinoctial, or from hot tropical countries, a 

 long-continued and uniform increase of heat. 



14. The ground-vegetation of various tropical and subtropical 

 regions are subject, sometimes, to a very considerable reduction of 

 temperature, owing to the powerful nocturnal radiation of heat ; 

 so that plants from thence should be carefully separated from 

 those which are impatient of any considerable diminution of 

 temperature. It is in this respect that mountain plants from 

 the tropics will bear being associated with those of subtropical 

 regions. 



15. As far as it is practicable, such plants only as agree in 

 their periods of vegetation should be associated together in any 



