1880.] Organisation of Fossil Plants of the Coal-measures. 553 



one. Tliis position has not escaped notice, but it was regarded as 

 accidental, but it now proves to be a normal one. The bundle begins 

 to appear in very young roots, as one or two very small vessels 

 developed in close union with the innermost cells of one side of the 

 cylinder within which it is located ; newer and larger vessels are 

 gradually added centripetally, until the bundle occupies a considerable 

 portion of the area enclosed by the inner bark cylinder. The re- 

 maining space is usually empty, but occasionally specimens are found 

 in which it is filled with small delicate cells that have escaped destruc- 

 tion. These represent what in the living Lycopods are liber-cells. 

 The outer cortical layer of the root, composed of well preserved 

 and rather thick walled cells, is usually separated from the inner 

 cylinder by a similar lacuna ; but in a few specimens the cells of this 

 usually destroyed middle bark are retained in good preservation. 

 They consist of very delicate thin- walled parenchyma, separated by a 

 sharp line of demarcation equally from the innermost and outermost 

 cortical cylinders. The number of the vessels in each of the vascular 

 bundles given off from any one section of a Stigmarian root is found to 

 vary but little, but they steadily increase, both in number and size, 

 with the size and age of the root. Young specimens of Stigmarian 

 roots are described, the smallest of which is not more than one-fifth of 

 an inch in diameter, and the vascular bundles of its small rootlets 

 consists each of from three to five minute vessels. In the largest 

 rootlets from old roots they number about forty, most of the additional 

 ones being of larger size ; intermediate examples exhibit a regular 

 gradation on all these points. 



The only living plants which possess rootlets with this structure 

 being LycopodiaceaB and Ophioglossse, and it being sufficiently clear 

 that the Lepidodendra belong to the former and not to the latter 

 order of Cryptogams, the existence of this Lycopodiaceous feature in 

 the rootlets of Sigillaria is another indication of the Lycopodiaceous 

 affinities of these plants. 



Many of the Diploxyloid forms of the Lycopodiaceous stems of the 

 Coal-measures have an abundant development of spiral or barred ceils 

 in their numerous medullary rays. Among living plants this 

 characteristic seems to be almost, if not wholly, confined to the Grym- 

 nosperms. 



Two important additional observations have been made in reference 

 to the structure of the curious Strobilus, Calamostachys Binneyana, 

 The exact mode of the attachment of its sporangia to the Equiseti- 

 form sporangiophores has been ascertained ; but what is still more 

 important, it has also been discovered that it is provided with both 

 micro- and macro-spores — an additional indication of its probable 

 Lycopodiaceous affinities, already suggested by other features of the 

 fruit. 



