INTRODUCTION. 



extremities tapering |;o a point and more or less thickened walls. Their 



tapering ends overlap each other, and in this way give greater strength 



and toughness to the tissue. 



H. The walls of contiguous cells are found to have pits or thin spots 



exactly opposite each other, but these do not amount to perforations, and, 



at least while the cell is in an active and growing state, there is no direct 



connection or passageway between the interior of one and that of 



another. The pits are usually plainly discernible under a microscope of 



high power. Fig. 1 represents a few wood-cells from Pine limber and the 

 comparatively large pits there shown, called bordered 

 pits. are characteristic of all the representatives of the 

 Pine family. 



10. By a process known as oxwox/x the sap passes from 

 one cell to another, and so on throughout the length of 

 tin- tree. 



1 1 . Among the cells are cert a i n channels or air-passages, 

 which are often so large as to be plainly visible to the 

 naked eve. They are known as t/ttc/s, and are formed 

 from large and blunt cells arranged end to end together, 

 and in time their end partitions become more or less 

 obliterated. Their walls are variously marked with promi- 

 nence and depressions disposed often with great regularity. 



Tn Fig. "2 are shown the cells, ducts, etc., as seen in the I>eech wood 



highly magnified. 



P-2. It would be interesting 



to dwell longer on the micro- 

 scopic structure of wood, and 



si udy its wonderful forms and 



arrangement; but we will have 



to leave that to the reader, 



who with his magnifier can see 



for himself considerable, even 



in the accompanying sect ions, 



although thinner sections are 



needed for high magnification. 

 I.']. Such in brief is the 



structure of what is known as 



the ( " fibro-vascular " system, 



which makes up the substance 



of wood. Its arrangement in 



t he stem may be in eit her one 



of two ways, and upon this is 



based tin- first division in the 



classification of 



Plants. 



Flowering 



FTO. 2. 



14. The Exogenous Stem. (L. ex from or outside of and yen us 

 origin) is characterized by having a central column of pith (made up 



na^nitii'd. ( From 



Fur. 1. \Voo(l-cells ,,f tin- Tine, slio\\ 

 IIoiiL'li's Klements of Forestry.) 



\<jr. 'J. Section (tangential) of Heecli wood, showing, /', /"', <'*<' 

 m, medullary ruvs cut across. Magnified i>ofi diameter-. |F 

 Forestry, i 



mis forms of cells, and 

 Houtrli's Kkments of 



