90 



VIEWS OF THE MICROSCOPIC WORLD. 



The large openings y y, &c., are spiral vessels, having a diameter of about one 

 two hundred and fiftieth part of an inch. The heavy and boldly defined lines 

 running lengthwise of the figure are the rays of cellular tissue which proceed 

 from the pith to the bark. 



Fig. 136. 



WHITE PINE. A transverse section of White Pine, magnified four hundred 

 times, is presented in figure 137. The cause of the lightness of the Pine is seen 



Fig. 137. 



at <i glance ; for the wood is as full of openings as apiece of lace-work, and con- 

 sists of nothing but a web woven -of the fine fibres of the cellular tissue. Across 

 the figure at the points a a, bands of cellular tissue are beheld, stretching from 

 side to side, and the structure is here more compact than in any other part of 

 the wood. These divisions are portions of concentric annual layers formed by 

 the compression of the cellular tissue. 



