102 PLANT LIFE 



thick and lignified walls, whether they are 

 specifically mechanical, or are discharging 

 other functions as well, such as that of 

 storing supplies of food in the trunk. An 

 enormous proportion of the wood of ordinary 

 trees consists, then, of thick -walled cells of 

 various kinds which are more or less intimately 

 knit together, with the result that the whole 

 possesses not only considerable strength but 

 also a high degree of resilience. This latter 

 quality differs greatly in different timbers, 

 but it is entirely the result of the properties 

 of the individual cell walls, combined with the 

 manner in which the cells themselves have 

 interdigitated with one another. 



An ordinary tree, by virtue of these pro- 

 perties of the wood, is able to withstand the 

 effects of a direct crushing stress far greater 

 than it will ever be called to meet in nature. 

 It has also, by virtue of its resiliency, the 

 faculty of recovering its position when it is 

 swayed or bent by the wind. 



As regards the great lateral branches of 

 large trees, their heavy weight of foliage and 

 small branchlets renders the need for power 

 of resistence and recovery from strains of 

 various sorts even more pressing. Some- 

 times, indeed, they prove inadequate, as when 

 a branch' becomes overloaded with fruit. In 

 the present year (1912) the great weight of 

 beech mast is causing many large branches 

 to bend down till they have come to rest 

 upon the ground, and in not a few instances 



