OF THE WOODY ZONE IN CALAMITE. 161 



Fig. 6 represents part of a tangential section, the letters 

 c and d being used to indicate the same parts as in the 

 last figure. We here see that the vessels (fig. 3 c) run from 

 one articulation or internode to the other, in the shape of 

 elongated tubes, arranged like the fibres of living Conifers, 

 and separated at intervals by numerous medullary rays (fig. 

 7 e) consisting of vertical layers of cells, arranged in single 

 series. The surfaces of the vessels in this section often 

 display no trace of structure ; but here and there we ob- 

 tained distinct evidence that their walls were strengthened 

 internally by woody reticulations. The intermediate pros- 

 enchymatous tracts (fig. 6 d) consist, as already stated, 

 of oblong cells (fig. 8) of fusiform shape, but which do not 

 exhibit, in this aspect, the regular serial arrangement that 

 is so conspicuous in the transverse section; medullary 

 rays appear almost, if not wholly, absent from this part 

 of the structure. In only two instances have I detected 

 anything that could be mistaken for such a ray ; and these 

 were possibly nothing more than a few linearly arranged 

 cells, shorter than the rest. 



On making a vertical section of a vascular tract (figs. 2 

 and 3 c) in the plane of a medullary ray (fig. 9), we dis- 

 cover that the vessels (9 c) are still regularly arranged in 

 parallel series ; and, on applying a high magnifying-power, 

 we find their surfaces to be covered with small reticulations, 

 arranged in an irregular order (fig. 12), but usually with 

 from three to four contiguous areolae between the two 

 sides of each vessel. These reticulated vessels very closely 

 resemble those seen in some varieties of Dadoxylon. The 

 reticulations have no central dot, consequently they must 

 not (asMr.Carruthershasalreadypointed out)be confounded 

 with the disks of true glandular fibre. This section reveals 

 the form and arrangement of the cells constituting the medul- 

 lary rays (9 e) . They have thin walls, and are arranged in 

 a muriform manner ; only the long axis of each cell is often 



8ER. III. VOL. IV. M 



