1890.] of the Fossil Plants of the Coal-measures, 



295 



other plants of the Carboniferous strata, we have had no evidence 

 until now that the same mode of growth ever occurred amongst the 

 Ferns. Now, however, this Cryptogamic family is shown to be no 

 longer an exceptional one in this respect. All the three great divisions 

 of the Vascular Cryptogams, the Equisetaceee, the Lycopodiacese, and 

 the Homosporous Filices of the primaeval world, exhibited the mode 

 of growth which is confined, at the present day, to the Angio- 

 spermous plants. A further interesting feature of the life of this 

 Ly g inodendron is seen in the history of the development of its con- 

 spicuous medulla. In several of his previous memoirs, notably in his 

 Part VI, the author has demonstrated a peculiarity in the origin of 

 the medulla of the Sigillariau and Lepidodendrian plants. Instead of 

 being a conspicuous structure in the youngest state of the stems and 

 branches of these plants, as it is' in the recent Ferns, and as in most of 

 the living Angiosperms, few or no traces of it are observable in these 

 fossil Lycopodiaceae. In them it develops itself in the interior of an 

 apparently solid bundle of tracheae (within which doubtless some 

 obscure cellular germs must be hidden), but ultimately it becomes a 

 large and conspicuous organ. The author has now ascertained that a 

 similar medulla is developed, in precisely the same way, within a 

 large vascular bundle occupying the centre of the very young twigs 

 of the Lyg inodendron. But in this latter plant other phenomena 

 associated with this development make its history even yet more 

 clear and indisputable than in the case of the Lycopods. The entire 

 history of these anomalous developments adds a new chapter to our 

 records of the physiology of the vegetable kingdom. 



Further light is also thrown upon the structure of the Heterangium 

 Grievii, originally described in the author's memoir, Part IV. This 

 plant presents many features in its structure suggesting that it too 

 will ultimately prove to be a Fern. The specimens described in the 

 above memoir, published in 1873, all possessed a more or less 

 developed exogenous xylem zone. But the author has now obtained 

 other examples in which no such zone exists. It is clear therefore 

 that in this, as well as in so many others of the fossil Cryptogams 

 of the Coal-measures, this exogenous development is a secondary 

 phenomenon — a product of a more advanced stage of growth. In 

 their younger states all these plants seem to approach nearer to their 

 recent representatives than they do in their later stages of growth. 



The author has now discovered the stem of a genus of plants 

 (Bowmanites), hitherto known only by some fruits, the detailed 

 organisation of which was originally described by him in the ' Trans- 

 actions of the Literary and Philosophical Society of Manchester,' in 

 1871. The structure of this new stem corresponds closely with what 

 is seen in Sphenophyllum and in some forms of Asterophyllites 

 (Memoir V, ' Phil. Trans.,' 1874, p. 41, et seq.). This discovery makes 



