154 PROPERTIES OF WOOD. 



rub against the main stem and against one another when the 

 wind blows and eventually become naturally grafted together or 

 to the main stem, so that the poles would grow into worthless 

 trees, they should be carefully pruned or removed in early 

 thinnings. 



On broadleaved stems in high forest, epicormic branches 

 (water-sprouts) are produced, when the stems are set free 

 from a dense crop ; this cannot be prevented entirely 

 by careful thinnings. As this premature development of 

 epicormic branches is usually due to the want of vigour in 

 their crowns, such stems should also be cut in thinnings in 

 preference to those clean-barked poles, which eventually 

 produce the finest trees. In standards over coppice, the 

 production of epicormic branches is normal after each 

 cutting of the underwood and then they should be pruned 

 carefully. 



Sapling-shake (Heisterknick) is a defective bend in the 

 stem of oaks at a height of about 6 feet from the 

 ground. It is so named, because it depends on the 

 planting of saplings of 6 feet, their usual height, in oak 

 woodlands. 



e. Defects in the Chemical Properties of Wood. 



The investigation of chemical defects in wood has been so 

 meagre, that only a few remarks on this subject can be 

 offered. Cieslar proved that the relative mass of lignin, as 

 compared with that of cellulose, in wood, depends on the 

 amount of heat and light to which the tree has been exposed. 

 Suppressed poles are, therefore, defectively constructed, for 

 they contain too great a percentage of cellulose ; it is reason- 

 able to assume that thus those economic properties which 

 depend on the sp. weight of wood will be prejudiced. By 

 lignification, science means the storing of lignin on the 

 cellulose walls of woody tissues, but in practice, the word 

 denotes the resting-phase of vegetation at the end of a growing- 

 season, the hardening of yearling shoots and of the last 

 annual woody zone, that are then said to be lignined. Sus- 

 ceptibility to early frost of insufficiently ligiiiiied tissues does 



