266 DISEASES OF TREES 



hand, the cambium of the stock is active, so that immediate 

 coalescence may take place between the callus-tissues produced 

 by its cambium and by the cambium region of the scion, and 

 when, on the other hand, the scion or bud is at the same time 

 inactive. The coalescence, in fact, demands a certain time. 

 Should the scion become active before coalescence has been 

 effected, or should its buds even be swollen at the time of the 

 operation, it withers in consequence of transpiration from the 

 young leaves before it can obtain a sufficient supply of water 

 from the stock. On this account the scions are prepared as early 

 as February, and are preserved in such a manner that by 

 repressing the tendency to growth as far as possible they will still 

 be inactive at the time when the stock has burst into leaf. As 

 is well known, budding is usually undertaken in summer, after 

 the new axillary buds have been formed, the buds being united to 

 the stock at a time when cell-division is still active in its cambium. 



The scion and stock are united in such a way that their 

 cambium layers are brought into as intimate contact as pos- 

 sible, care being also taken that no considerable interspaces 

 are left between the cut surfaces of the wood. According to 

 Goppert's investigations, coalescence is due to two distinct 

 processes, for not only does union occur between the cambial 

 layers, or the callus-tissues that are produced from them, but also 

 between the cut surfaces of the wood. The cells of the paren- 

 chyma, both of the medullary rays and of the wood, are stimu- 

 lated to divide, and so form a connecting or intermediary tissue, 

 which completely fills up the space between the two cut surfaces. 



If the operation has succeeded and the scion has grown, the 

 latter is in future supplied with the raw food-materials that are 

 absorbed from the soil by the roots of the stock. On the other 

 hand, the plastic materials that are elaborated in the scion 

 nourish the cambium both of the scion and the stock. Of 

 course the new elements that are produced by the cambium 

 cells of the scion are the characteristic elements of the scion, and 

 similarly with regard to the elements produced by the cambium 

 of the stock. The plastic materials produced in the scion afford 

 assimilable nourishment to both scion and stock, just as cow's 

 milk may serve as nourishment not only to a calf but also to a 

 child. But the latter does not on that account assume the pecu- 



