34ft PROFESSOK W. C. WILLIAMSON ON THE PLANTS 



epiphlceum or corky layer, and the mesophloeum or middle 

 layer of the bark. In fig. 4, which represents a vertical 

 section of the same tissues, only enlarged to about twice 

 the size of fig. 3, the cells of the epiphlceum and mesophloeum 

 (4 a) are still more regular and distinct. In this section 

 they are usually square, and arranged in interrupted vertical 

 rows, which sometimes tend a little outwards towards the 

 exterior of the bark. In the horizontal section their 

 square contour is less obvious; they exhibit more of the 

 corrugated aspect seen in the dried bark of a recent Arau- 

 caria. Fig. 3 b, is obviously the endophloeum or inner bark, 

 which is of considerable thickness. Its true character is 

 better seen in the vertical section, fig. 4 b, where its dis- 

 tinctness from the mesophloeum is very obvious. As in the 

 recent Araucaria, it consists of some cellular tissue, along 

 with a vast number of the elongated ducts which are so 

 conspicuous in the inner bark of the recent plants, and 

 which, I presume, are the laticiferous vessels. In the hori- 

 zontal section (fig. 3 b), numbers of these vessels are faintly 

 seen, ascending from below in an oblique manner. In the 

 vertical section, the cells of the epiphlceum have an average 

 diameter of about the --—- of an inch. Those of the meso- 



& O O 



phlceum are smaller, and a little more elongated vertically. 

 The diameter of the laticiferous vessels is about ^ioo ^^ ^^ 

 inch. 



Nothing can be more distinct than the line of demarca- 

 tion between these tissues and the woody zone (c). In the 

 horizontal section (fig. 5\ this zone exhibits the ordinary 

 aspect presented by coniferous wood from the coal measures. 



It consists wholly of pleurenchyma or woody fibre, 

 arranged in radiating lines (fig. 5 c), and separated at in- 

 tervals by intervening medullary rays (fig. 5 d). There 

 are no concentric lines of growth, such as are seen in 

 recent Araucariae and other coniferae. This feature of 

 many of the fossil woods of the coal, measures has been 



