284 Field, Forest, and Wayside Flowers 



tapering to a point at either end (Fig. 79). Most 

 of these run lengthwise of trunk or boughs, and in 

 / their walls there are circles or 

 ovals at regular distances 

 apart. Each of these is a 

 little plate of very thin tissue, 

 set into the partition between 

 two tracheids, and framed on 

 both sides by a ring-shaped 

 bulge in the tracheid-wall. 

 The whole affair looks like 

 a tiny circle surrounded by a 

 halo. When the tracheids 

 were young and full of pro- 

 toplasm, plant-fluids were 

 drawn through the thin spots, 

 and thus a vital communica- 

 tion was kept up through all 



FIG. 79. Tracheids of the 



fir-tree. (Magnified.) the maturing tissue. But by 

 the time the tracheid is fully developed the proto- 

 plasm which has filled it disappears, and the mature 

 wood of a cone bearer contains little else but a 

 film of water on the tracheid-walls. So most of 

 the "bordered pits" are no longer useful in the 

 vegetable economy. 



The Coniferae combine the utmost grandure of 



