DBFBOTS AND DNBOITNDNBSa. 31 



the circumference. Sometimes two or more such cracks occur, to 



Fig. 1. 



Ueart-ShMke, 



which the special name of compound lieart-shalce or star-shake^ may- 

 be given as distinguished from the simple heart-shake. The origin 

 of the heart-shake is always the drying up and consequent shrink- 

 ing of the tissue at the centre at the stem; As the surrounding 

 tissues do not contract at the same time, the central mass splits 

 along one or more lines of least resistance, that is to say, along 

 medullary rays or radially. As with advancing age the shrinking 

 continues, the cracks extend outwards as well as grow wider. The 

 drying up and shrinking of the inner tissues may be due to old 

 age, or to weak growth induced by an unfavourable soil or situation 

 or by forest fires. Hence heart-shakes always begin and are 

 worst at the foot of the affected trees. Sometimes, if owing to 

 one or more of these causes there is a predisposition to this de- 

 fect, a heart-shake may be produced in a previously apparently 

 cound tree by the shock of the fall when the tree is felled, or even 

 by the mere lurch given by the tree as it begins to fall. Strong 

 winds must obviously aggravate heart-shakes. As heart-shaken 

 logs dry, the cracks continue to extend themselves. To minimise 

 this danger, the logs must not be barked, and must be allowed to 

 season as slowly as possible. A simple device that is nearly always 

 successful in arresting the extension of narrow cracks is to drive a 

 thin wooden wedge into the end of the log just in front of, and 

 across the path of, each such crack. Owing to the position and 

 origin of a heart-shake the wood on the sides of the cracks will 

 generally be found to be more or less decayed, unless the shake 



