GRAFTING AND NURSERIES. 213, 



little callus ; others produce it in great abundance. The 

 same facts have been observed with different varieties of 

 vines; some, and these give the greater percentage of takes 

 when grafted, produce callus freely and abundantly (Ber- 

 landieri, Cinerea, Rupestris du Lot, Vialla, Cabernet- 

 Sauvignon) ; others (Solonis, Folle-blanche) always produce 

 it slowly, and in small quantity; the latter evidently do not 

 knit as free or as easily. 



But, independently of the nature of each variety, the for- 

 mation of the knitting tissue also depends on the influence 

 of certain external circumstances. According to Millardet, 

 it is produced more freely and in greater abundance at a 

 temperature of 20 C. According to recent researches bv 

 Gouirand, it is between 25 and 35 C. ; above 35 C. the 

 graft suffers. Between 15 and 20 C. the formation of callus 

 is very slow. In short, what is required is a fairly high 

 and, above all, even temperature. This explains why scions 

 stratified in light warm soil, deep enough for the temperature 

 to be subject to only slight fluctuations, bear the largest pads 

 of callus. 



The degree of humidity of the soil has a -very marked 

 influence. If cuttings, or even scions, have their lower 

 extremities immersed in water, no knitting tissue will ever 

 form. Scions stratified in sand, kept very damp by frequent 

 watering, will develop buds, but no or very little callus will 

 form. This frequently happens when grafted cuttings are 

 stratified in too damp moss. In almost dry but fresh sand, 

 on the contrary, enormous pads ,of callus develop rapidly. 

 Excessive humidity around the joint prevents the formation 

 of knitting tissue; and it is in soils containing from 5 to 10 

 per cent. ,of water that it is most easily formed. 



On the other hand, aeration considerably accelerates its 

 development. The cells in course of rapid growth respire 

 abundantly, they therefore require well aerated surroundings, 

 rich in oxygen. This explains why cuttings buried deeply 

 in compact soil do not form any callus at their base, and 

 why grafted cuttings planted in stiff soils do not succeed 

 well. When the joint of a newly-made graft is enclosed in 

 an indiarubber tube, preventing access of air, the scion 

 sometimes grows for a long while, although no knitting tis- 

 sue is produced. 



(b) Effects of Grafting. "Affinity." Connection being 

 established between the vascular bundles of stock and scion, 



