426 THE GARDENER. [Sept. 



(copal); and for the hydro-carbons, caoutchouc and gutta-percha. It 

 may be here mentioned that the milky secretions of our common 

 wild-flowers, such as of the Dent de lion or Dandelion, Sow thistle, 

 (Sonchus crispus), Spurges (Euphorbia), or Celandine (Chelidonium 

 majus), may be regarded as caoutchouc. 



Leaves, by exhalation or transpiration, give off in vapour the water 

 of the sap : sun-heat and wind are both causes of this natural process, 

 and a fresh supply of water will be necessary to restore the equil- 

 ibrium j but it does not go on so rapidly during dull quiet days, and 

 the gardener therefore does not then water his plants so freely as 

 might be otherwise necessary to do after they have been exhausted 

 by sun-heat, nor does he water his plants during sun-heat, nor in 

 windy weather, as it would only tend to increase the exhalation or 

 transpiration, which, when excessive, carries off so much heat from 

 the plant. It has been said that one of the uses of garden-walls is to 

 keep off the wind, and so lessen the exhalation of plants. Du Breuil 

 says that watering fruit-trees growing in the open air, except during 

 their first year of planting, does more harm than good, and to stone 

 fruit-trees is destructive to their roots. 



Some tuberous-rooted plants may be propagated by their leaves 

 without buds on them, as Gloxinia gesnera, tuberous Begonia, and 

 many succulent plants. The process by which this is induced is 

 very simple, its direct cause more difficult to explain. The leaf is de- 

 tached from its parent plant, placed flat on the surface of a pot con- 

 taining silver-sand, and the veins are cut or broken, and an artificial 

 node or axil is produced ; the leaf is pegged down, or kept down in 

 its place, and with the usual appliances of heat, warmth, moisture, 

 and a bell-glass over it, it soon emits roots which will form small 

 bulbs, even at the edges of the leaf, and the green fleshy part of 

 the leaf will perish. 



Leaf- buds consisting of wrapped-up leaves are formed, in temperate 

 and cold climates, at the end of the stem or branch, in the autumn, 

 or in the axils on the stem, where the leaves or leaf-stalks are situate;* 

 the mode or plan on which the bud is formed is called "vernation." 

 These buds or eyes, as they are called, can be easily cut out from the 

 stem of a plant, such as the Vine, and be induced to grow in warmth ; 

 or they can be cut out from one tree and placed in the stem of 

 another tree when the sap is flowing — and to this faculty is due the 

 practice of budding fruit-trees, as well as Eose-trees on the Briar, and 

 which will to some extent supersede the old system of grafting. 



* Trees and shrubs in hot climates do not produce buds ; the interval between 

 the formation and evolution of the bud is so short as not to need this protec- 

 tion for the shoot. 



