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 PKOGRESS OF MICKOSCOPICAL SCIENCE. 



The Organization of AsterophyUites. — In au abstract piiblislied in 

 a recent number of the P.R.S., Professor Williamson gives tbe follow- 

 ing account of his own views of its structure and relations : — On two 

 occasions he dii-ected attention, in the ' Proceedings of the Royal 

 Society,'* to the structure of some stems which appeared to him to belong 

 to the well-known genus Asterophijllites, briefly pointing out at the same 

 time their ajjparent relations to a strobilus of which he had previously 

 published figures and descriptions f under the name of Volkmannia 

 Dawsoni. In the present memoir he gives a detailed exposition of 

 the various parts of the plant, including the roots, rootlets, stems, 

 branches, leaves, and fruit, in different stages of their development. 

 This is done chiefly in two modifications of the primary type — one 

 from the Lower Coal-measures of Oldham in Lancashire, the other 

 from those of Burntisland. In its youngest state, the Oldham form 

 first appears as a mere twig, having a central fibro-vascular bundle 

 enclosed in a double bark. The vascular bundle consists entirely of 

 vessels which are chiefly, if not wholly, of the reticulated type. When 

 divided transversely, it presents a triangular section, the triangle having 

 long narrow arms and very concave sides. The bark is already dif- 

 ferentiated into two layers, and has its exterior deeply indented by 

 three lateral grooves — one opposite to each concave side of the vascular 

 triangle. The outer layer is prosenchymatous, with vertically elongated 

 cells ; the inner one consists of cylindrical parenchyma arranged in 

 radial lines, the cells being also elongated vertically. As the plant 

 grew, successive vascular layers were added exogenously to the exterior 

 of the vascular axis. Each layer consisted of a single linear row of 

 vessels, which were of large size opposite the concavities of the triangle, 

 and small where they approached its several angles. The radial arrange- 

 ment of those in the several growths was equally regular ; they were 

 disposed in single radiating series, new laminae being intercalated 

 peripherally as the stem grew. These radiating laminfe were sepa- 

 rated by small medullary rays. Owing to the fact mentioned, that 

 the laminfe radiating from the concave sides of the central triangle 

 consisted of much larger vessels than those radiating from its angles, 

 three or four such growths sufficed to convert its concave sides into 

 slightly convex ones, whilst a few more such additions converted the 

 vascular axis into a solid cylindrical rod. At this stage its transverse 

 sections appeared definitely divided into six radiating areas — three of 

 large ojjen vessels radiating from the sides of the primary triangle, 

 and three of small ones proceeding from the sides and extremities of 

 the angles. When these growths have thus given a cylindrical form 

 to the vascular axis, a change takes place in its further development. 

 Concentric growths again begin to form, but in them all the vessels 

 are of almost equally small diameters : hence the abrupt termination 



* Vol. XX., pp. 95 and 435. 



t ' Transactions of the Literary and Philosophical Society of Manchester,' 

 third series, vol. v., 1871. 



