No. 467.] STUDY OF THE SALICACEE. SII 
In transverse section the distribution, form, and compounding 
of the vessels impart to the structure an appearance quite 
similar to that found in the Rhamnacez. This very striking 
resemblance is likely to result in confusion unless very careful 
attention is given to details; and the likelihood of error from 
this source is all the more probable when it is observed that 
there is also a strong similarity of structural detail in radial 
section. It is, however, not our purpose to discuss these resem- 


Fic. 9.— Salix alba. Tang tial section. X 52. 
blances at the present moment, since the essential differentia- 
tions of the two families will be sufficiently emphasized by their 
separate study. In the Salicacez the vessels give to the entire 
Structure a high degree of porosity which is extended more or 
less uniformly to the entire thickness of the gr owth — (Figs. 
, 7). This general law is subject to variation in detail. Thus 
