DEVONIAN PLANTS. 25 



aud coutaiuiug areas of altered structure where the tissue appeared as iu the other 

 specimens. Teu measurements gave au extreme variation of from 30 /< to 70 /< and an 

 average diameter of 51 /'. 



In addition to these I have also examined a special series of sections taken from 

 plants in different degrees of silification. In all of these, the characters above noted were 

 present, but the size of the false cells appeared to present greater variation. It is from 

 one of these that the photo-micrograijh (Plate I fig. 1) was taken. I have also noted 

 that, on the Avhole, the false cells are of greater size in those specimens where the crystal- 

 lization of the silica was carried to the highest degree. The same fact is apparent by 

 comparison of the measurements in Nos. 1-4 as above stated. From this it would appear 

 clear to us that the degree of crystallization, and hence, the redistribution of the organic 

 matter, depend upon and are directly related to the previous operation, as well as the 

 extent, of decay in the organic structure. Therefore, the more advanced the condition of 

 decay at the time when silica was deposited, the larger will be the crystals and false 

 cells dependent upon them. The significance of these facts, as bearing upon the true 

 character of Oelluloxylon, will hardly admit of question. 



Celluloxylon. 



The original specimens from which were cut the sections of Celluloxylon examined by 

 me, were obtained by Sir Wm. Dawson from the collection of Prof. H. M. Clarke, of Amherst, 

 Massachusetts having been found in the Hamilton Group (Middle Brian), Canandaigua, 

 New York.' This is described as " A silicified trunk showing in cross-section large and 

 somewhat unequal, hexagonal cells, with an appearance of lines of growth caused by 

 concentric bands of smaller cells. No medullary rays. The longitudinal section shows 

 either cells superimposed in vertical rows, or a sort of banded prosenchymatous tissue 

 but the structure is much masked by the crystallization of the quartz. 



" Additional specimens received from Prof. Clarke show that the appearance of rings 

 of growth is caused by large cells disposed in concentric, narrow bands between the 

 wider bands of fine, fibrous tissue. In the longitudinal section, three bands of large cells 

 appear to be parenchymatous and not vascular. There are no medullary rays, but rounded 

 patches of cellular tissue appear here and there in fibrous layers." 



The original specimens from which the sections were cut have been again examined 

 by me. With one or two exceptions, all of these pieces are so curved as to show that they 

 are parts of concentric layers about one-fourth of an inch thick. A concentric lamination 

 in the stem, similar to that of N. Lngani, is evident. All of the specimens are of the same 

 kind with respect to silicification, and show that the alteration has been carried on to a 

 high degree. The texture is finely granular and, under a lens of low power, the material 

 appears to be very finely crystalline, quite similar to that found in large stems of iV. 

 Logani, where the crystallization is also advanced. A certain longitudinal striation, of not 

 very pronounced character, may also be detected. The absence of any radial markings is 

 conspicuous, as noted in the original description. This, in the highly altered condition of 

 the material, does not of necessity imply their absence from the original structure. 



■ Quart. Ju'I. Geol. Soc, May, 1881, p. 302. 



Sec. IV, 1889. 4. 



