UPON PLANT-HOUSES. 81 



suffei" from excess in this respect, and the hope of their flowering 

 will be frustrated ; indeed, it may be taken as a rule, that the 

 processes of vegetation and fructification are not the result of a 

 uniform continuance of these conditions. Plants frequently require 

 strong heat and moisture for their free growth and preparation for 

 blossoming, while to ensure this latter stage they must have more 

 light and a drier heat. A sudden change from a favourable com- 

 bination of circumstaAces to one less so, will also produce this 

 effect. Considering the multifarious exigencies of each particular 

 sort of plant, how difficult, rather how impossible, to meet 

 them in detail ! All we can do is to individualise our cultures 

 by means of numerous plant-houses, each adapted for a limited 

 assemblage of those plants, which correspond most in their various 

 conditions of life. 



The modern labours of Dove, Quetelet, Kreil * and others, on 

 the dispersion and motion of caloric, exhibiting a mighty 

 system of causes and effects which influence all living creatures, 

 cannot fail to be productive of the greatest practical results in 

 agriculture and gardening. The time may come, perhaps, when 

 the difference of zones will to a certain extent be overcome in 

 our gardens. But, as yet, our cultures are subject to severe 

 difficulties, not the least of these being the complete reversion 

 of seasons in our hemisphere, as compared with the other, 

 and the difference in the periods of development, depending 

 thereon ; not to mention the countless local differences which 

 influence the vegetation of the same hemisphere and the 

 same latitude. Hence it would be of the greatest use if an 

 attempt were made to furnish the art of horticulture with an 

 appropriate geography of plants, combining besides a general 

 account of the distribution of heat and the climate, also a 

 minute detail of the local peculiarities of those parts of the 

 world which possess a peculiar Flora. It is my humble opinion 

 that considerations of this sort have not been sufficiently attended 

 to in practical horticulture, in as much as we collect together 

 plants from the most different parts of the world and crowd them 

 together indiscriminately, within one and the same building. 



The following two tables, which I have extracted from Dove's 

 work, will serve to convey to the eye what I have briefly sketched 

 out above. 



* Dove, Connexion of the Changes of Atmospliericai Heat with the 

 Development of Plants, Berlin, 1846, 4to. ; Movement of Heat in Strata of 

 Different Geognostic Characters, ISiS ; Tables of Temperature, with Remarls 



VOIi. IX. G 



