IIG NOTES ON NEMATOPHYTON CRASSUM PENHALLOW. 



TRANSVERSE SECTION.* l'^« 



558 



The transverse section ;is a wliole shows considerable diversity of 

 strnctnre, obvionsly dne to alteration in the process of decay and the 

 subsequent formation of siliceous crystals. In one part the cell walls 

 and all cell cavities are sharply defined. The cells are fairly uniform in 

 size, ranjiing from 23 /< to 4(> /^ with an average of 34 /<. The walls are 

 very black and 3.8 /.t thick. The cells are, as a rule, rather remote, be- 

 ing distant 3.8 fA. to 49.4 /^, thus giving to the structure, as a whole, a 

 very loose, open cliai-acter. Tiiere is very rarely an indication of in- 

 tercellular tihuni'uts where now and then a large one, running trans- 

 versely, has survived th(^ otherwise general disintegration of the hyphte. 

 All tlie intercellular spaces are (»ccu[)icd by a tine cellular ai)p('arance, 

 due to the disposition of a very Ihin layer of tlie altered carbonaceous 

 substance upon the surfaces of small crystals of silica. 



In the other i)arts (see Fig. 7), '-I.|!^', the large round cells are obvious, 

 but the walls have become thickened in an irregular manner and have 

 lost their sharp outlines in a marked degree, while they are commonly 

 coinun-ted with one another by coarse lines of carbonaceous substance 

 in such a way as to make the intercellular spaces appear like large 

 an<l imperfectly formed parenchyma cells with irregularly thickened 

 walls. All the intercellular spaces are occupied by a mass of tine crys- 

 tals, having the appearance of a very tine cellular tissue. 



In yet a third area (see Fig. 5), ^,],^j', the round cells of the first have 

 almost absolutely disap])eared. Only here and there can a trace of one 

 be found. They have been wholly replaced by typical CcUuloxylon struc- 

 ture, indistinguishable from that found in the original type specimens 

 of that genus. That these three conditions do not represent normal 

 structures is at once obvious from the transitional conditions to be found 

 within the same section. 



RADIAL ? SECTION (^^fy). 



In this the Celluloxylon structure is very prominent. In many places 

 it shows derivation from tubular cells, the position of these latter being- 

 very obvious under a low po\ter. As in the transverse section, there is 

 no evidence of intercellular filaments. Karely, obscure indications of 

 open areas are met with. 



TANGENTIAL? SECTION {^j%). 



The general structure is the same as in the radial section except that 

 we here meet with well-detined evidence of oi)en areas. These are irreg- 

 ular in form, somewhat numerous, and filled with a mass of very fine 

 crystals of silica, about which carbonaceous matter has been deposited, 



*The numbers given refer (niuncrator) to my laboratory nnniber and (deuomiaa^ 

 tor) to the number as given in the collection of the U, S, Geologicivl Survey, 



