238 DISEASES OF TREES 



" Preventitious " buds are also to be reckoned amongst the 

 regenerative phenomena that follow on injuries to trees, and 

 which compensate for portions that have been lost. Only a 

 limited number of the axillary buds of a shoot develop in the 

 following year to form new shoots. The majority of these buds, 

 and especially such as are situated in the axils of the bud-scales 

 and of the undersized leaves towards the base of the shoot, 

 remain imperfectly developed, and do not, as a rule, shoot out in 

 the following year. It is these which constitute the dormant 

 eyes, or " Preventitious Buds " of Theodore Hartig, so called 

 because they are present on any given portion of stem from the 

 first year of its existence. Only under certain circumstances do 

 these burst forth into new shoots, e.g. epicormic * branches and 

 the like. Preventitious buds is a term employed in contradistinc- 

 tion to adventitious buds, the latter indicating neiv buds that are 

 formed under certain conditions.-)- 



These axillary buds may remain alive for a hundred years and 

 more, especially in the case of trees with a smooth rind, such as 

 the beech, &c. 



It is only as regards apical growth that the preventitious buds 

 (Fig. 136, a) are inactive, for they display a peculiar form of 

 growth in length, which Theodore Hartig has called " Inter- 

 mediary Growth." Each year the delicate vascular bundles, which 

 extend from the medulla to the buds (Fig. 136, #), increase in 

 length to the same extent as the portion of the stem on which 

 the buds are situated increases in thickness. Such growth is 

 perfectly analogous to the growth of the sucker-roots of Viscum 

 album, or to the growth in length of medullary rays. The bud- 

 axis that is embraced by the stem possesses its own cambium, J 

 at the point where it crosses the cambium of the stem. 



The cambium of the axis of the bud, which divides at the 

 same rate as the common cambium of the stem, annually pro- 

 duces two portions of tissue namely, a larger one on the inside 



* [Shoots which develop in this way on the trunk are known as Epicormic 

 shoots. Such shoots are very common on old Elms, &c. ED.] 



f [" Adventitious," because they arise in places where they would not 

 normally be expected. ED.] 



| [Embryonic tissue, which adds new tissues to those already existing in the 

 suppressed bud. ED.] 



