240 JOURNAL OF FORESTRY 



9. The dimensions of the rays was determined by measurements on 

 the tangential face of the wood. 



10. The number of bordered pits represents an average count for 

 several cells. 



The three woods chosen for special consideration represent widely 

 separated families. The bald cypress, Taxodiiim distichum (L.) Rich., 

 from the Pinaceae, represents the coniferous type; the tulip poplar, 

 Liriodendron tidipifera L., from the Magnoliacese, represents a diffuse 

 porous dicotyledon; and the white ash, Fraxinus americana L.. from 

 the Oleaceae, represents a ring-porous wood. 



Turning to a consideration of the special examples, figure 1 shows 

 a transverse section of the normal stenuvood of Ta.vodiuiii distichum 

 magnified to 150 diameters. In the upper portion of the figure the 

 thin-walled spring tracheids may be seen, while the lower portion is 

 occupied by the thick-walled strengthening cells which were formed 

 later during the growing season. In the section here represented the 

 thick-walled tracheids occupy about 38 per cent of the area. The dark 

 vertical line bisecting the right side of the print pictures a uniseriate 

 storage ray cut longitudinally. Figure 2 shows a cross-section of a 

 brash cypress under the same degree of magnification. It will be 

 observed that the same types of cells are present. The only new 

 features represented in the section are the storage parenchyma cells 

 which, owing to their resinous content, have registered black on the 

 photographic print. Such structures were present in the first section 

 mentioned, but do not appear in the field selected for the illustration. 

 The most striking difference between the two woods is in the volume 

 of the summerwood. In contrast to 38 per cent in the first, only 2 

 per cent can be so classed in the second. The relative thickness of 

 the tracheid walls is as equally indicative of the brash character of 

 the latter as is brought out in Table 1 which includes comparative data 

 of the two woods. In the second column is recorded the specific gravity 

 for the two specimens, and it will be observed that the stronger stick 

 is about twice as heavy as the weaker or brash one. The same pro- 

 portion is maintained in regard to the thickness of the cell walls. Those 

 in the summerwood average .009 mm. and .004 mm., respectively, 

 and a like relation exists in the springwood where the measure is 

 .004 mm. and .002 mm. In other words, tlie thick summer cells in 

 the brash wood are only equal in thickness to the thin-walled spring 

 tracheids in the stronger one. Reference has already been made to the 



