PRINCIPLES OF GARDENING. 53 



These considerations must influence our minds in the growth of 

 orchidaceous plants, which grow in their native woods on living plants ; 

 and it has been a question with me, whether in our green-houses they 

 are supplied with their requisite earthy salts ; the whole matter requires 

 to be experimentally worked out with care. 



Notwithstanding our plants may have every material requisite 

 for their nutrition and growth, yet they must be under the influence 

 of physical forces. Every plant requires a definite degree of heat. 

 One plant requires for its successful cultivation a heat little short of 

 90° Fahr., which we can obtain artificially ; another plant lives at 

 the tops of the snow-clad mountains, where it freezes every night 

 in the year. Heat we can generate, cold we cannot regulate — or 

 rather we never have regulated it as yet, though we could as easily 

 circulate cold water as hot in our pipes. The learned Professor of 

 Botany at Florence told me, that he found it impossible to grow 

 Alpine plants in that city. 



The changes which take place in the interior of plants are caused by 

 the action of light, which enables them to reduce the carbon products, — 

 such as gum, starch, and woody fibre, — from the carbonic acid of the 

 atmosphere. The regulation of the amount of light to various plants, 

 requires judgment and skill. Hard-wooded plants, as the peach and 

 nectarine, require the fullest exposure to light ; and I do not like my 

 vines to have any shade. Some delicate plants like shade in the 

 hottest part of the day. This is accomplished, in this country, by a 

 light woven material to cover the glass ; but at Paris by thin wooden 

 laths painted green and fastened together by wire, so that the whole 

 can be rolled up and taken away in autumn, when the intensity of 

 the light begins to be feeble. Sometimes we wash over the glass 

 with a pale blue tint to modify the warmer rays. In my garden all 

 materials for shadiag are avoided as much as possible, but plants 

 which do not bear a strong hght are placed in a north aspect, exposed 

 to the light of the sky, but not to the direct rays of the sun. 



Experiment and experience has taught me to use more light; 

 even for ferns than has hitherto been considered beneficial, but then 



