140 COLD BORDERS CAUSE SHANKING. 



temperature it had gained on the surface, parts with it to the soil as it 

 passes down, and thus produces that bottom heat which is so essential 

 to plants, although so few suspect its existence. 



This necessity of warmth at the root undoubtedly explains in 

 part why it is that hardy trees, over whose roots earth has been 

 heaped or paving laid, are found to suffer so much, or even to 

 die ; in such cases, the earth in which the roots are growing is 

 constantly much colder than the atmosphere, instead of 

 warmer. 



It is to the coldness of the earth that must be ascribed 

 the common circumstance of Vines that are forced early 

 not setting their fruit well, when their roots are in the 

 external border and unprotected by artificial means ; and to the 

 same cause is often to be ascribed the shanking or shrivelling 

 of grapes, which most commonly happens to Vines whose roots 

 are in a cold and unsunned border. 



Mr. Knight long since mentioned an important fact connected with 

 this subject: — " It is well known," he said, "that the bark of Oak-trees 

 is usually stripped off in the spring, and that in the same season the 

 bark of other trees may be easily detached from their alburnum, or 

 sap-wood, from which it is, at that season, separated, by the interven- 

 tion of a mixed cellular and mucUagiuous substance ; this is apparently 

 employed in the organisation of a new layer of iibre, or inner bark, the 

 annual formation of which is essential to the growth of the tree. If, at 

 this period, a severe frosty night or very cold winds occur, the bark 

 of the trunk, or main stem, of the Oak-tree becomes agaiu firmly 

 attached to its alburnum, from which it cannot be separated tUl the 

 return of milder weather. Neither the health of the tree, nor its 

 foliage, nor its blossoms, appear to sustain any material injury by this 

 sudden suspension of its functions ; but the crop of acorns invariably 

 fails. The Apple and Pear-trees appear to be affected to the same 

 extent by similar degrees of cold. Their blossoms, like those of the 

 Oak, unfold perfectly weU, and present the most healthy and vigorous 

 character ; and their poUen sheds freely. Their fruit, also, appears to 

 set well ; but the whole, or nearly the whole, falls off just at the period 

 when its growth ought to commence. Some varieties of the Apple and 

 Pear are much more capable of bearing unfavourable weather than 

 others, and even the Oak-trees present, in this respect, some dissimi- 

 larity of constitution." [Hort. Trans., vi. 229.) 



It is also the coldness of the soil which causes the production 

 of roots upon the stems of the Vme in a hot damp Vinery ; 



