316 THE POPULAR SCIENCE MONTHLY. 



through fifty-two natural orders of plants. Sixteen of these are 

 heavier than water, and have a specific gravity varying from 

 1'3020 in the black iron wood of southern Florida to a white oak 

 (Quercus grisea) of New Mexico with the wood only slightly 

 heavier than water namely, 1/0092 for its specific gravity. It is 

 interesting to note in passing that all these sixteen kinds of wood 

 that will sink in water are natives of southern Florida, a semi- 

 tropical region, and the South and West regions, none of them 

 growing in the Mississippi Valley or east of it. 



The black ironwood above mentioned as having the heaviest 

 wood is in many respects a striking contrast with the giant red- 

 wood (Sequoia) of California, which is not only the largest of our 

 trees, but its wood is among the lightest, it having a specific 

 gravity of only 0'2884, or about one fourth as heavy as the iron- 



FIG. 3. CROSS SECTION OF ASH WOOD. 



wood, which latter is a small, gnarly tree of no value as building 

 timber. 



It was said that there are four hundred and twelve species of 

 timber receiving treatment in the census report, and therefore 

 it is appropriate to show the peculiarities of the one that stands 

 midway of this long list as regards its specific gravity, and espe- 

 cially so as it is one of the more common sorts and a very valu- 

 able timber for many purposes namely, the ash (Fraxinus). 



Fig. 3 shows the appearance of this wood as seen looking upon 

 the smooth surface of the end of a stick of timber. It is a decided- 

 ly porous wood, as indicated by the minute, light dots which are 

 arranged in a series of curved belts in the engraving. 



This leads us naturally to consider somewhat in detail the 

 general make-up of a stem or trunk of a tree. The primary divi- 

 sion of the parts is into the wood and the bark. The latter is 



