VEGETABLE SAP. 127 



envelope. Some former, and many modern, botanists 

 consider these callosities as no other than obstructions 

 of the returning- sap ; others conceive that they are 

 fibres projected from the buds and shoots above, which 

 are arrested in their progress down, and accumulating 

 above the constriction cause the distortions in question. 



From many and repeated observations made on 

 the effects of ligatures on various sorts of trees and 

 shrubs, and daily in view for several years past, it is 

 quite evident, that the swellings, both above and 

 below, beg-in to be visible very soon after the spring- 

 growth commences ; and that they appear to be 

 nothing more than that part of the vital membrane 

 confined by the band, venting- itself above and below, 

 and forming- the protuberances alluded to. If a single 

 wire be used, the swellings on each side are nearly 

 equal : if the band be of the usual width of a shred, 

 the prominences on each side are nearly equal on 

 some trees, but on others that on the upper side is 

 considerably larger than the one below. (Fig. 36.) 



It is quite obvious, that if there be a procession of 

 either sap or fibres from the superior to the inferior 

 parts of the stem, a ligature would certainly produce 

 a swollen margin on the upper side ; and did the 

 tumour at any time of its growth contain simple sap 

 only, no doubt would remain of the cause ; but this 

 is never the case ; the interior is invariably found to 

 be either imperfect or perfect wood, that is, either 

 cambium or alburnous matter. This, indeed, to those 

 who believe that the sap is " organisable," is BO 



