INJURIES DUE TO FROST AND HAIL 33 



healed, as shown by the accompanying figure, and afterwards 

 no more branches were formed on the upper side of these 

 branches, and only comparatively few on the lower side ; as 

 a result these four branches were literally starved to death, 

 owing to lack of food and water. The three large lower 

 branches, being sheltered by the upper ones, were perfectly 

 healthy and bore an abundance of foliage and flowers when 

 the tree was cut down. 



Glassy fir is the name given by Schrenk to the appearance 

 of glassy or polished portions of the trunk of the balsam fir 

 (Abies balsamea), when cut with a cross-cut saw. These 

 portions are perfectly smooth and shiny, as if they had been 

 planed, and are conspicuous as contrasted with the normal 

 roughened surface produced by the saw. Some of these 

 patches extended from the heart to. the sap-wood, others 

 formed irregularly circumscribed spots usually surrounding 

 healed-over portions of old branches. Where the patches 

 were isolated they were generally near some check. In all 

 cases the sap-wood had the glassy appearance. All the 

 specimens examined were cut during the months of February 

 and March, when the temperature was 32 F., or much 

 lower. 



A series of experiments showed that the glassy appearance 

 was due to the presence of frozen water in the wood. Wherever 

 the wood-cells were filled with ice the saw made a clean 

 polished cut, and the fibres were not torn as is usually the 

 case, the ice acting like imbedding material, paraffin, etc., 

 in sustaining the weak cell-walls during the operation of 

 cutting sections. In cooling, the sap-wood just within the 

 bark would freeze first, and the cooling would gradually 

 extend inwards, hence the sap-wood presents a uniform 

 glassy appearance. The distribution of glassy patches along 

 the lines of former branches is accounted for by assuming 

 that the lowering of the temperature would take place more 

 quickly along such channels as are in communication with 

 the outer portions of the trunk. 



From a practical lumbering standpoint, glassy fir cannot 

 be considered as a defect, as it has been in some instances 

 before its origin was clearly known. 



Schrenk, H. Von, 'Glassy fir,' Sixteenth Ann. Rep. 

 Missouri Bot. Gard. (1905). 



C 



