258 Essay on Physiological Botany : — ' 



motion by the warmth of the sun early in spring, its strength 

 is lost before the sun can reach its roots to put them in equal 

 motion, which causes the blossoms to drop off and the shoots 

 to become stagnant." 



The above quotation is susceptible of strong comments, but 

 I proceed to notice Mr. G. Bliss's Practical Treatise on the 

 Cultivation of Fruit Trees {19,25). At page 60., on Grafting, he 

 denies any influence of the stock on the scion engrafted there- 

 on, and says, " the fund of vegetable matter above ground 

 must be filtered through the roots," &c. ; and that " the stock 

 partakes of the nature of the scion ; for there cannot be an 

 existing doubt but that the roots, veins, fibres, or whatever 

 they may be called, strike from the scion into the stock, and 

 run downwards to the extremity where the sap flows." He 

 then gives an instance of a variegated jasmine being budded 

 on a common o-reen one, and several of the buds below the 

 one inserted became variegated. 



Mitchel in his Dendrolbgia^ published in 1827, denies the 

 circulation of sap, and designates the branches, fronds, buds, 

 and leaves, as caterers to the tree. 



Van Helmont's experiments on the willow tree, which in- 

 creased 119 pounds in five years, and only wasted 3 ounces of 

 earth, show that the sap to sustain the tree, with its increase 

 of 1 19 pounds, could not be derived from the earth, or else a 

 greater waste must have taken place. Or must all that in- 

 crease be attributed to the distilled water he gave it? 



I now offer some instances of practical operations occurring 

 yearly in the plashing of quickset hedges, which is done by 

 the common labourer, who cuts out all such shoots as are not 

 wanted for the layers ; the latter he cuts nearly off", leaving no 

 more than a bit of bark, and a small thin portion of wood on 

 one side, the substance of which, in the case of a strong layer, 

 is not more than a common leather strap ; the thinner it is, the 

 better for the layer. Here we see the epidermis, cortical body, 

 liber, wood, corona, and pith, all severed, and, in some casesj 

 part of the stump or stock cut off^, leaving 4 to 8 in. space be- 

 tween the body of the stool and layer. Yet we see the layers 

 in a full healthy state of vegetation, with an exudation of sap 

 from the lower end, many days before the gaseous atmospheric 

 influence acts upon the stock or stump. In this case I do not 

 see that it is probable, and scarcely possible, that the rami' 

 fications of the layer, to the extent of 10 or 15 ft., could be fed 

 and supported by the small, strap-like, connecting splice at the 

 bottom. 



The most superficial observer must have seen moderate- 

 sized elm trees vegetate strongly the first, and weakly the se- 



