GRAFTING AND NURSERIES. 211 



transformed into cork, and, in one or more layers, form a 

 corky protective envelope, more or less resistant, com- 

 pletely surrounding each protuberance, and generally unite 

 with the corky layers of the cane. 



On the upper section of the stock the same phenomena 

 occur, but are not so apparent, and appear much later. The 

 reason of this is that the cane has no tendency to protect 

 wounds on its upper extremity. The same applies to the 

 whole vine. The exposed section made on a cane when 

 pruning never gets covered with callus, the surface of the 

 cut dries up for a variable length, its channels get blocked 

 with gum, etc., but the living cells do not form any cork 

 or other tissue. Every one has seen that cuttings stratified 

 in cool sand or earth form callus excrescences at their 

 base ; it is seldom that there is any at the top. It is only 

 when placed in contact with another section that the heal- 

 ing tissue is produced more abundantly. In all cases it 

 is produced in the same manner as on the scion, or on the 

 base of the cutting, and at the expense of the same cellular 

 layers. 



If an excision be made on the side of a cane, the knitting 

 tissue at first forms on the upper part of the excision, then 

 on the sides, and finally lower part; it is formed in greater 

 abundance on the part of the excision looking downwards, 

 following the sides, and later on with more difficulty forms 

 on the part looking upwards. 



A longitudinal cleft from the top downwards, on a vine- 

 cutting squarely cut off (such as is prepared for an English 

 cleft graft), forms knitting tissue on the lateral sides, but 

 none, or scarcely any, on the transverse section from which 

 the cleft starts. On the oblique section of the splice of a 

 stock prepared for the whip-tongue graft, the knitting tissue 

 seems to form with as much difficulty as on a transverse section 



Finally, the knitting tissue forms with greater ease and in 

 greater abundance near the node than on the internode. 



These protuberances of healing tissue knit when brought 

 in contact with each other, by the juxtaposition of the sections 

 of stock and scion. The younger they are when brought in 

 contact, that is to say the less suberfied the external cells 

 are, the more perfectly the knitting takes place. It results 

 from this that the two sections must be brought as close 

 together as possible. The cells directly produced by the 

 multiplicalion of the generative layers knit. One of their 



