500 Forestry Quarterly 



On account of the distiirbed political conditions, the splendid cedar 

 forests south of Fez and Mekn^s cannot be exploited, 



T. S. W., Jr. 



V exploitation des Forets au Moroc. Revue des Eaux et For6ts, June 1, 

 1916, pp. 178-81. 



BOTANY AND ZOOLOGY 



In a highly suggestive article Dr. Leon 



Causes discusses structures developed in both ani- 



oj mals and plants, developed to perform the 



Tree Form function for which they exist, starting from 



the idea that "the continuous use of an 



organ conditioni^ its progressive adaptation to the purpose for which 



it exists, and vice versa the non-use debilitates it." Tree forms 



may be explained in this way. The bast and woody tissue in the 



full-grown individual, the coUenchyma in its development period 



serve to strengthen the plant organs. 



Trees are frequently not circular, but have an oval croFS-section, 

 the diameters in west-east direction being longer than in north- 

 south direction, a result of the prevailing winds. Small trees 

 fastened so that they can sway only in one direction increase their 

 diameter mainly in this direction. Trees securely fastened to 

 poles in all directions increase in diameter much less than those free 

 to move, and if unfastened rapidly make up for delay, if they are 

 still capable of standing up. On those parts of stem and branches 

 which are continually or mainly required to withstand tensile 

 stress a different wood structure is formed than in those under 

 compression, hence one may speak of "tension wood" and "com- 

 pression wood," or according to the color (when fresh) of "white 

 wood" and "redwood." Woodchoppers correctly call the wind- 

 ward side of the tree, the ' ' soft ' ' side, the opposite the "hard ' ' side. 

 It is in tensile strength that the soft side excels, the hard side excels 

 in resistance to indentation. 



A leaning tree develops red wood on the lower, tensile wood on 

 the upper side ; similarly, a one-sided branch development produces 

 red wood. With the change of the load a change in the character 

 of the wood takes place. Owing to the response to tensions, the 

 quality of the wood in the lower portion of the trunk is mostly 

 superior to that of the upper portions ; at the insertion of branches 



