262 DISEASES OF TREES 



In the case of that tree the axillary buds of the primary leaves 

 preserve their vitality until the formation of bark begins, usually 

 about the fifth year, when they perish, and with them the power 

 of producing stool-shoots is lost. 



Those American pines which have three leaves in the sheath, 

 for instance P. rigida, retain the power of producing stool-shoots 

 till a late age. This is owing to dwarf shoots being developed 

 partly in the whorls, and partly on the main axis midway 

 between the whorls. These dwarf shoots grow each year to an 

 extent corresponding to the growth in thickness of the stem, and 

 produce but few leaf-fascicles. It is these that give rise to an 

 abundant growth of stool-shoots. On account of the absence of 

 dormant eyes that are capable of producing shoots, the regene- 

 rative power of the stools of conifers is a very limited one, if 

 we except those cases that have been quoted. The formation of 

 adventitious buds in the callus of wounds is also very exceptional, 

 and it is only in the case of the silver fir that I have occasionally 

 observed new bujis and shoots produced from the callus of the 

 stool. On the other hand, it frequently happens that the stools 

 of conifers more especially those of the silver fir, spruce, and 

 larch, very rarely those of the Scotch pine live for several 

 decades, and form callus more or less energetically along the 

 edge of the cut surface, so that in certain cases the whole of the 

 transverse section may be occluded. It is probable that the 

 formation of callus on the stool is generally due to the natural 

 grafting of the roots of the tree that has been felled (the 

 nourished stem) with those of an adjoining tree (the nourishing 

 stem). There is, however, no getting over the case quoted by 

 Th. Hartig, where a larch-stool showed a growth of callus 

 notwithstanding the fact that the tree had stood in a large gap 

 in a wood, so that the possibility of nutriment being transferred 

 from a neighbouring tree was absolutely precluded. This case 

 can only be explained by supposing that in the course of years 

 the reserve materials stored up in the roots and stool were 

 dissolved and applied to the nourishment of the cambium. 



If the cortex and cambium have not been destroyed for some 

 distance back, by the drying up and decay of the wood, the 

 stools of dicotyledons develop a callus and numerous buds 

 during the year succeeding that in which the tree was felled. 



