306 CALAMARIEAE. 



this kind, as we know, and as Hick and Cash 1 have well shown, may make 

 its appearance in a similar manner in plants very far removed from one 

 another, if only they have certain adaptations in common, such as growing 

 in water or in wet places ; it can hardly therefore be employed to determine 

 a genus or a group, or, if so, only in peculiar circumstances. 



Further, Renault * has described several species which he assigns to 

 Astromyelon, and has figured three of them, Astromyelon augustodunense, 

 Ren., A. dadoxylinum, Ren. and A. nodosum, Ren., on the three plates of his 

 work. He too, like Williamson, insists especially on the absence of nodes, 

 and remarks that the structure of the wood shows the greatest resemblance 

 to that of Arthropitys, being essentially distinguished from it only by 

 the presence of the 'bois centripete,' which is closely connected with the ' bois 

 centrifuge ' and is surrounded by it. From this remark, and also from the 

 circumstance that Renault cites in this connection Schenk's 3 figure noticed 

 above, and will not allow it to be an Arthropitys, I perceive that the ' bois 

 centripete' does not mean here the entire primary bundle, as it usually does 

 elsewhere, but only its initial strand, and further that on the transverse 

 section at least there is no difference to be observed between Renault's 

 Astromyelon and his Arthropitys. We saw above that in the same section 

 the initial strand may be preserved in some bundles, and may be replaced 

 by a lacuna in others. The absence of nodes would th'en be the only 

 remaining difference. It is not for me to determine what is the true account 

 of the matter, for I have had no opportunity of properly studying the 

 remains in question. It is to be hoped that Renault himself will soon 

 give us some further explanation. The structure of the rind is only known 

 in one of the three species described by him, Astromyelon augustodunense 4 . 

 There it is entirely parenchymatous, and the inner portion which sur- 

 rounds the ring of wood is traversed by groups of dark-coloured cells, 

 which lie in front of the wedges of wood, and are explained as ' canaux ' or 

 ' cellules a gomme.' The intercellular spaces of the middle portion of 

 the rind are only of moderate breadth, and are separated from one another 

 by thick plates of tissue consisting of several layers of cells. 



It is evident from what has now been said that nothing at all certain 

 can be stated at present respecting Astromyelon, and that it is possible that 

 different plant-forms have been united under this name. The structure 

 of the wood affords not the slightest ground for comparing this genus with 

 Marsilea, as is done by Williamson 5 ; if there are points of resemblance, and 

 I am myself unable to find them, they must be of purely external character. 

 Renault 6 even has not ventured to draw any conclusion from the cir- 

 cumstance that these remains are often associated at Grand' Croix with 



1 Hick and Cash (1), p. 91. 3 Renault (13). * Zittel (1), p. 237. 4 Renault 



(13), t. 7, ff. i, 2. Williamson (1), xn. 6 Renault (13). 



