564- Summary View of the Progress of Gardening, 



as to the humidity, dryness, lightness, or shadiness of the local- 

 ities in which they were found. Hence, plants of the most con- 

 trary habits are crowded together in our plant-houses, or all 

 exposed to an equal degree of the influence of the sun in the 

 open garden." The writer then goes on to show that succulent 

 plants, and those "which produce a great abundance of leaves, 

 and consequently expose a large extent of leafy surface to the 

 atmosphere," require intense light ; while those which have 

 scanty foliage, or leaves with very porous surfaces, and which are 

 consequently liable to great evaporation, are generally found in 

 shady places. The gardener, if" he be well acquainted with phy- 

 siological botany, may often determine from the structure of the 

 plant, what degree of light is best adapted for it ; but, in default 

 of this knowledge, he must have recourse to the collectors who 



... 



discovered the plants in their native habitats. In the second ar- 

 ticle (p. 131.), the importance of light to the Cactus tribe, and to 

 the genera Mesembryanthemum, Agave^ Stapel/a, &c., is pointed 

 out, and enforced by stating the fact (by no means an uncommon 

 one), of large plants of cactuses being found growing in the 

 back part of stoves, where they get no direct light, and where, 

 though they have attained a large size, they show no signs of 

 flowering ; while the same species in the front of a stove, and 

 trained close under the glass, will flower profusely, when of a 

 comparatively small size, and at an early age. In a third article 

 on the same subject (p. 155.), the injurious effects of the sun's 

 rays on various species of Cape heaths under glass are remarked 

 on ; and, as we have stated (p. 476.), a canvass, for occasionally 

 shading these plants, is strongly recommended. The influence of 

 light on orange trees, the writer finds a matter of greater diffi- 

 culty to determine ; but he thinks the houses intended for this tribe 

 should admit more light than they generally do at present, and 

 that the plants should be retained in them throughout the year. 

 The fourth article (p. 179.) treats of the camellia with reference 

 to light, condemns the practice of growing it in mixed collections, 

 and recommends a shaded position, in which the camellias "are 

 naturally, or can be artificially, screened and protected from the 

 more violent rays of the sun." Pelargoniums, like the heath 

 and the camellia, require a house for themselves, but they must be 

 supplied with a great degree of solar light. Under the head of 

 miscellaneous green-house plants, the writer classes the genera 

 Acacia, Banks/a, Protea, Fuchs/r/, and "all those green-house 

 plants which possess no affinity in character or habit " with the 

 five classes already treated of; viz. succulents, heaths, orange 

 trees, camellias, and pelargoniums. Most of the plants of 

 this miscellaneous class will thrive best in a house where abun- 

 dance of light is supplied. Objections, it will be said, will be 

 made to having five houses for five kinds of green-house plants, 



