PLUNGflNG.- 435 



those cases where the air is kept, by artificial means, shaded 

 and uniformly damp. The extent of these changes gardeners 

 are hardly aware of; a few years ago I found in a conservatory, 

 in the months of May and June, that the temperature of the 

 soil in a small flower-pot was as low as 40° at one period of the day 

 and as high as 90° at another period. In a dry summer day, 

 when the leaves are perspiring freely and requiring an abund- 

 ance of water from the roots, the latter are placed in contact 

 with a substance whose moisture is continually diminishing; 

 or in a greenhouse, where the pots are syringed, the heat of 

 the earth in contact with the roots is lowered by a copious 

 evaporation from the sides of the pot, jiist when, in nature, the 

 bottom-heat should be the greatest. The evil consequences of 

 this are well known to gardeners, who however often neglect 

 taking sufficient precautions to prevent it. Greenhouse plants 

 exposed to the open air in summer always suffer severely from 

 the irregular condition of the sides of the pots, whence the 

 common practice of plunging them in the earth, for the purpose 

 of bringing them into the condition of plants growing in the 

 open ground. 



This is, however, attended with some disadvantage, for the 

 plants root, through the bottom of the pots or over the edges, 

 among the earth in which they are plunged, and when taken up 

 in the autumn for removal they must have all such roots cut off 

 again, for there are no means of bringiug them withia the limits 

 of a pot. For these and similar reasons, no good gardener will 

 expose his greenhouse plants to the open air in summer, {/ he 

 can help it, unless they are duplicates, or unless there is some 

 object to be attained very different from the strange notion 

 that they are rendered more hardy by the process. The effect 

 that is really produced upon them is to give them a sort of 

 artificial winter in summer, that is to say to expose them to a 

 period of comparative rest from growth, which in many cases is 

 useful, or to expose them more fuUy to the sun at a time when 

 they are ripening fruit. Mr. Knight assures us that by having 

 the sides of their pots exposed fuUy to the air, the taste and flavour 

 of the Peach and Nectarine, and still more of the Strawberry, 

 are greatly improved, and the Fig-tree in the stove is made to 



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