132 PR0GKES8 OF MICROSCOPICAL SCIENCE. 



of Asterophyllites, with which group the author believes the fruit to 

 be related, notwithstanding the peculiarity of its sporangia and 

 sporangiophores. The author is confirmed in his conclusion that 

 this fruit is not Calamitean by his having already described the 

 structure of a true Calamitean strobilus, from an example in which 

 the central axis retains most accurately the arrangements of tissues 

 characteristic of Calamitean stems (Manchester Transactions, 1870). 

 A type of stem to which the author had previously assigned the pro- 

 visional generic name of Amyelon is now shown to be the root or 

 subterranean axis of AsterophylUtes, specimens being described in 

 which clusters of rootlets are given off, in irregular order, from various 

 points of the exterior of the branching roots. The latter have no 

 medulla ; but in the centres of several of them the author finds the 

 peculiar triangular fibro-vascular bundle so characteristic of Astero- 

 phyllites ; and in all remains of the same trifid origin of the vascular 

 layers may be traced in the peculiar curvatures assumed by the 

 vascular laminae as they proceed from within outwards. The bark 

 consists of two layers : the inner one is composed of ordinary paren- 

 chymatous cells, often of considerable size : the outer one consists of 

 irregular piles or columns of cells, disposed perpendicularly to the 

 sui'face of the bark, and with their tangential septa in close contact 

 and in parallel planes. The lateral or radial boundaries of these piles 

 of cells are more strongly defined than the transverse septa. In tan- 

 gential sections of this outer bark, each of these radially-disjjosed 

 columns of parallel-sided cells appears as a single thick- walled paren- 

 chymatous cell, whose aspect, in common with that of its neighbours, 

 is that of ordinary coarse parenchyma. Such sections exhibit no 

 indication of the radial elongation of these cells seen in radial and 

 transverse ones. On re-examining the inner bark, we discover the 

 exj)lanation of these appearances. Many of the larger and more 

 peripheral of the cells of the latter are seen to be undergoing division 

 by the development within their walls of secondary cell-partitions, 

 which are parallel with those of the radially-disposed columns. It 

 appears obvious that each of the latter was primarily one of the cells 

 of the inner bark, which has become elongated radially, and at the 

 same time divided into a linear series of compressed cells by the 

 growth of a succession of secondary divisions, all of which were more 

 or less tangential to the periphery of the stem. 



The author directs special attention to the genetic activity of this 

 inner bark ; the cells of its inner surface were obviously instrumental 

 in producing the successive circumferential additions to the primary 

 vascular axis, whilst those of its outer surface increased the diameter 

 of the outer bark in the way just described. 



After comparing these plants with living forms, the conclusion is 

 arrived at that the nearest parallel to the structure of their stems is to 

 be found in Psiloium triquctrum ; whilst their general affinities are 

 regarded by the author as Lycopodiaceous rather than Equisetaceous. 

 The exogenous aspect of tlieir successive vascular growths is, if 

 possible, more conspicuous than in most of the other Carboniferous 

 Cryptogams. 



