BUDS, BAEK, AND PITH. 267 



.rotting their tender and incipient contents. 

 Some, underneatli their waterproof covering, 

 include softest down, which provides warmth 

 and secures protection against wintry cold. 



The function of bark is to the stem and 

 branches of a tree what the bud-scales are to the 

 bud. Bark is first a delicate, thin coating of 

 somewhat harder cellular tissue than that which 

 composes the interior of the stem. Inside this 

 is a still more delicate envelope of cellular tissue, 

 called the inner bark. As the outer coating 

 thickens and hardens, the inner one also becomes 

 thicker and naore substantial, and both serve as 

 protecting membranes to the sap-wood, the latter 

 serves to protect the heart-wood, and the heart- 

 wood the delicate central column of pith. The 

 larger the surface or superficies, whether of trunk 

 or branch, presented to the cold, the thicker and 

 rougher and warmer becomes the enveloping and 

 protecting bark. It is in its early stage that 

 the pith of a plant needs the fourfold protection 

 afforded by the incipient heart-wood, sap-wood, 

 inner bark, and outer bark. It is then that the 

 function of pith is most vital, for it' is the central 

 and principal canal through which the sap flows 



