1872.] 



among the Plants of the Coal-measures. 



437 



Lancashire specimens are covered with sparse, but very distinct hairs, that, 

 unlike the ramentaceous form common amongst ferns, are perfectly cylin- 

 drical. Whilst I am thus inclined to express my conviction that M. 

 Renault is correct in his views respecting Zygopteris, I find it increasingly 

 difficult to distinguish fragments of ferns from those of Lycopods, as also 

 fragments of petioles from those of roots. 



Mr. Nield and Mr. Whittaker, of Oldham, have just supplied me with 

 two magnificent stems of Calamites of large size. The pith is absent 

 from both, except some slight traces at the node of one of the specimens. 

 I find on dissecting these matured stems that the remarkable arrangements of 

 the vascular structure seen in plate 23. figure 2 of my memoir on Calamites 

 almost entirely disappear in the more external of the exogenous growths. 

 The conspicuous vertical laminae of cellular parenchyma (my primary 

 medullary rays), which separate the woody wedges, rapidly diminish in size 

 as they proceed from within outwards, becoming more or less like the 

 secondary or ordinary medullary rays represented in my fig. 5 . Many of 

 them, however, retain the evidence of their primary medullary origin in 

 their unusual length, and by consisting of two, or even three, vertical series 

 of cells instead of one, as is usual with the secondary rays. The vessels 

 pursue their longitudinal course across the node undeflected in any direction, 

 save where they bend aside to allow the passage outwards of vascular bundles 

 going off to the aerial branches*, as represented in my figures 13 and 38. 

 Thus in the exterior parts of these large stems the ligneous zone exhibits little 

 or no indication of the presence of a node, except what these divergent bundles 

 afford. I find that these bundles slightly increase in size as they proceed 

 from within outwards, showing that they share in the exogenous additions 

 made to the exterior of the ligneous zone ; in one of my stems that zone 

 has a circumference of seven inches, and the other of six and three 

 quarters. It is in the former one that I find the nodal bundles ; but I have 

 not seen one of these organs whose actual diameter exceeds three sixteenths 

 of an inch, confirming my previous statements respecting the compa- 

 ratively small size of the aerial branches. As in my previously described 

 examples, these bases of branches exhibit no separation of the vessels into a 

 circle of wedges like those of the parent stem. The persistent growth of 

 the vascular bundles just described seems to indicate more permanent rela- 

 tions between them and the central stem than I once thought probable. 

 There appears to be a close approximation to uniformity in the number of 

 the woody wedges of these large stems ; one of mine contains 85, and the 

 other 83 such. Mr. Binney counted 73 in his large specimen (Joe. cit. 

 pi. 2. fig. 1). In the thin, young, woody cylinder represented in my fig. 

 19, the mean diameter of which was slightly overan inch, the number was 

 also about 80. This close resemblance between stems so different in age 

 and size again illustrates another of my previous statements, viz. that age 



* This condition is very correctly represented in plate 3. fig. 3 of Mr. Binncy's 

 memoir on Calamites (Palieont. Soc.). 



