CANKER. 



of those similarly cultivated. The golden pip- 

 pin, the oldest existing variety of the apple, is 

 more frequently and seriously attacked thai 

 any other. The soil has a very considerable 

 influence in inducing the disease. If the sub- 

 soil is a ferruginous gravel, or if it is not wel 

 drained; if the soil is aluminous, and effective 

 means are not adopted to free it of superabun- 

 dant moisture, the canker, under any one of 

 these circumstances, is almost certain to make 

 its appearance among the trees they sustain. If 

 an old worn-out orchard is replanted with fruit 

 trees, the canker is almost certain to appear 

 among them, however young, ami vigorous they 

 were when first plantejgU-fiow inducive of this 

 disease is a wet, retentive subsoil, if the roots 

 penetrate it, appears from the statement of Mr 

 Watts, gardener to R. G. Russell, Esq., of Che- 

 quer's Court, in Buckinghamshire. A border 

 beneath a south wall had a soil three feet and 

 a half in depth, apparently of the most fertile 

 staple ; twice remade under the direction of 

 the late Mr. Lee, of the Vineyard, Hammer- 

 smith. In this the trees, peaches and nectar- 

 ines, flourish for the next three or four years 

 after they are planted, but then are rapidly de- 

 stroyed by the canker and gum. The subsoil 

 is a stiff sour clay, nearly approaching to a 

 brick earth ; and the disease occurs as soon as 

 it is reached by the roots of the trees. (Gar- 

 dener's Magazine, vol. vi. p. 617.) Pruning has 

 a powerful influeuce in preventing the occur- 

 rence of canker. I remember a standard rus- 

 set apple tree, of not more than twenty years' 

 growth, with a redundancy of ill-arranged 

 branches, that was excessively attacked by this 

 disease. I had two of its three main branches 

 removed, and the laterals of that remaining 

 thinned carefully, all the infected parts, at the 

 same time, being removed. The result was a 

 total cure. The branches were annually regu- 

 lated, and for six years the disease never reap- 

 peared. At the end of that time the tree had 

 to be removed, as the ground it stood upon was 

 required for another purpose. John Williams, 

 Esq., of Pitmaston, from long experience con- 

 cludes that the golden pippin, and other apples, 

 may be preserved from this disease by pruning 

 away, every year, that part of each shoot which 

 is not perfectly ripened. By pursuing this 

 method for six years, he brought a dwarf golden 

 pippin tree to be as vigorous and free from 

 canker as any new variety. (Trans. London 

 Hort. Soc. vol. vi. art. 64.) 



All these facts unite in assuring us that the 

 canker arises from the tree's weakness; from 

 a deficiency in its vital energy, and consequent 

 inability to imbibe and elaborate the nourish- 

 ment necessary to sustain its frame in vigour, 

 and much less to supply the healthy develope- 

 ment of new parts. It matters not whether its 

 energy is broken down by an unnatural rapidity 

 of growth, by a disproportioned excess of 

 branches over the mass of roots, by old age, or 

 by the disorganization of roots in an ungenial 

 soil; they render the tree incapable of extract- 

 ing sufficient nourishment from the soil, con- 

 sequently incapable of developing sufficient 

 foliage, and therefore unable to digest and ela- 

 borate even the scanty sap that is supplied to 

 them. 



256 



CANKER. 



The reason of the sap becoming unnaturally 

 saline appears to be, that in proportion as the 

 vigour of any vegetable declines, it loses the 

 power of selecting by its roots the nourishment 

 congenial to its nature. M. Saussure found in 

 his experiments that the roots of plants grow- 

 ing in saline solutions absorbed the most of 

 those salts., that were injurious to them, evi- 

 dently because the declining plant lost the sen- 

 sitiveness and energy necessary to select and 

 to reject. Thus, when plants of Polygonum 

 Persicaria and of Bidens cannabina were grown 

 in a solution containing sulphate of soda (Glau- 

 ber salt), acetate of lime, and chloride of sodium 

 (common salt), they altogether rejected the 

 acetate of lime; but when grown in a solution 

 of sulphate of copper and acetate of lime, they im- 

 bibed the latter abundantly. Now, sulphate of 

 copper M. Saussure found to be the most dele- 

 terious to the plants of all the salts, in a solu- 

 tion of which he plunged their roots. Suppos- 

 ing the portion originally in solution to be 100, 

 the proportions of each absorbed were as fol- 

 lows : 



Pa. 



I Chloride of sodium .... 10 

 < Sulphate of soda .... 6 

 (.Acetate of lime - .... 

 C Sulphate of copper - - - - 34 

 i Acetate of lime ..... 31 



M. Saussure also found, that if the extremi- 

 ties of the roots were removed, the plants ab- 

 sorbed all solutions indiscriminately. (Saus- 

 sure's Re'cherches Chimiques sur la Vegetation, 260.) 

 An ungenial soil would have a debilitating 

 influence upon the roots in a proportionate, 

 though less violent degree than the sulphate 

 of copper; and these, consequently, would 

 absorb soluble bodies more freely, and without 

 that discrimination so absolutely necessary for 

 a healthy vegetation ; so the other most essen- 

 tial organs of nutrition, the leaves of the weak- 

 ened plant, would promote and accelerate the 

 disease. These, reduced in number and size, 

 do not properly elaborate the sap ; and I have 

 always found that, under such circumstances, 

 hese stunted organs exhale the aqueous parti- 

 cles of the sap very abundantly, whilst their 

 lower of absorption is greatly reduced. The 

 sap, thus deficient in quantity and increased in 

 acridity, seems to corrode and affect the vascu- 

 ar system of the tree in the manner already 

 described. These facts afford us most impof- 

 ant guides in attaining the desired objects, the 

 ?revention and cure of the disease. If super- 

 uxuriance threatens its introduction, the best 

 remedy is for the cultivator to remove one of 

 he main roots of the tree, and for him to be 

 jarticularly careful not to add any fertile addi- 

 ion to the soil within their range. On the 

 contrary, it will be well, if the exuberant growth 

 shows its necessity, for the soil to be reduced 

 n fertility by the admixture of one less fertile, 

 or even of drift sand. If there is an excess of 

 )ranches, the saw and the pruning-knife must 

 )e gradually applied. It must be only trees of 

 weak vital powers, such as the golden pippin, 

 hat will bear the general cutting of the annual 

 shoots, as pursued by Mr. Williams. A new 

 ngorous variety would exhibit itself in the 

 bllowing year in the production of new wood. 

 Having completely headed down, if the can- 



