1S46.J Remarks on the Slrudure of Wood. 287 



ring is formed of two parts, the first which is filled with large tubes 

 and is the first growth of the wood for the year; the second is 

 more compact and is perforated by the secondary tubes or sap 

 vessels, and which are arranged in lines nearly parallel with the 

 medullary rays. In the general arrangement of these parts there 

 is quite a strong resemblance to the oaks. 



Fig. 2, is a transverse section of the elm. (Uhnus Americana.) 

 It will be observed at once that the structure of the elm is quite 

 different from the chestnut, the serges of primary pores are dif- 

 ferent, and especially are the secondary ones arranged in a mode 

 as different as possible. There is in fact a very beautiful appear- 

 ance in this arrangement. So far as my own observations ex- 

 tend this peculiarity of the secondary tubes or vessels is not found 

 in any other wood; the red elm resembles this in some respects, 

 still it is not difficult to distinguish them from each other. 



Fig. 3, is a section of the paw-paw tree. The wood is yel- 

 lowish; the primary tubes very close and the secondary in nar- 

 row and rather interrupted lines, approaching to parallelism with 

 the annual layers. The bark of this tree is close and compact, 

 traversed by the medullary rays arranged in pointed groups, con- 

 verging to the outside. 



No. 4, is a section of bass wood. It is doubtful whether it is 

 possible to make the usual separation of the sap vessels into 

 primary and secondary. They are exceeding small, but very nu- 

 merous. The rnedidlary rays also, are exceeding thin and dis- 

 tinct, only for short distances. The wood as is well known is 

 very close grained and compact, although it is one of our 

 lightest woods. The medullary rays of the bark are arranged 

 very much as in the paw-paw, and which seem to form the 

 corky matter which intervenes between the converging groups. 

 In most woods the external cracking of the bark is occasioned by 

 its medullary rays, — or rather the irregular longitudinal lines in 

 which the baik cracks are determined by the groups or clusters 

 of rays. It is by no means true that this peculiar arrangement 

 of the rays in the bark universally prevails — for it is quite com- 

 mon to find the bark made up of rings or deposits arranged in 

 ]>arallelism with the annual layers of the wood. I find in fact as 

 much diversity existing in the structure of the bark as in the 

 wood, so much so that a section of the bark itself and alone 

 would be suflficient to determine the species. I am well aware 

 that it is necessary in putting forth a new doctrine to be guarded, 

 and especially not to claim for it too much importance. I do not 

 mean therefore to assert that genera and species can be determined 

 always by an inspection of a transverse section of the stem or 



A siasjle row of vessels appear to mark the commencement of the year, 

 but the vessels themselves are but little larger than the secondary ones. 



