INCREASING STEIKE OF HERBACEOUS GRAFTS. 



29 



2nd. Preparation of scion-bud. Many operators, before 

 cutting the scion-bud, begin by cutting the petiole of the leaf 

 F, as close as possible to the bud B, placed at its base 

 in a a! (Fig. 38). Many failures in herbaceous grafting 

 are simply due to this defective method. Clarac has made 

 a whole series of interesting experiments on this subject. In 

 the first group of experiments, the petiole of the leaf was 

 cut as close as possible to the bud B, at a a'; success 

 middling. 



In the second group the petiole was cut at b b', at about 

 half its length ; numerous failures. In the third group, the 

 petioles and the limb of the leaf F were left intact ; com- 

 plete failure. Finally, in a fourth group the whole of the 

 petiole was preserved and a part of the limb c c , only left 

 attached to it. It was about J inch in diameter ; almost 

 complete success (Fig. 38). 



These curious re- 

 sults may easily be 

 explained. In the 

 first series the sec- 

 tion of the petiole 

 a a, determines the 

 surface evaporation 

 very close to the 

 scion-bud B. 



The latter there- 

 fore desiccates be- 

 fore having had 

 time to form its 

 knitting cambium. 

 In the second series 

 of experiments the petiole was cut further away from the bud 

 B ; but as this petiole is formed of a very vascular tissue, the 

 desiccation took place rapidly, and communicated itself to 

 the bud before it had time to knit. In the third series of 

 experiments the 'limb of the leaf was entirely preserved, 

 forming a large surface of evaporation and respiration, and 

 the bud B was destroyed, not being able to furnish the leaf 

 with the necessary nutritive element before the knitting 

 took place. In the fourth series of experiments, on the 

 contrary, the portion of the leaf preserved was not large 

 enough to cause very great evaporation, and yet was enough 

 to prevent the immediate desiccation of the petiole, and 

 therefore that of the bud before the knitting was completed. 



. Preparation of scion-bud. 



