48 UNITED STATES GEOLOGICAL SUBVEY— TERTIARY FLORA. 



seen in fig. 12 a, enlarged, they are either simple from the point of attachment 

 or forked once or twice, slightly tumescent at the point. Their distribution in 

 bundles along an axis is perhaps more analogous to that of rootlets of creep- 

 ing rhizomas, and the presence of thread-like filaments of this kind upon the 

 left branch of the specimen, plate Ixi, fig. 15, evidently part of Selaginella 

 falcata, might confirm this supposition; but there is no great analogy between 

 the characters of thread-like rootlets and those of this plant, for these are too 

 regular in their form, their divisions, and their curve in the same direction. 

 It may be that we have here, and in these two plants, the submerged and 

 the floating part of the same species ; that as it happens in some Phsenoga- 

 mous plants of the present flora, as, for example, in Nasturtium lacustre, the 

 immersed leaves are laciniate while the emerged ones are entire, I have, 

 however, vainly searched among species of Lycopodiacece of our time for any 

 traces of abnormal divisions like these ; even Lycopodium inundatum has the 

 leaves of the immersed branches entire. On another side, some creeping 

 species of Selaginella have at the base of the stems, or upon the stolons, a 

 kind of tendrils, generally filiform, sometimes dichotoraous, divided toward the 

 ends, and the divisions slightly inflated. This character is marked in Sela- 

 giwlla Mertensii, S. apus, but more distinctly in S. microphylla of Cuba, whose 

 tendrils are shorter and sometimes subdivided at the end in six or eight 

 branches. From this it appears that these two forms described above may 

 be parts of a species of creeping Selaginella, the stem, stolons, and tendrils 

 being represented on jjlate Ixiv, figs. 12, 13, the branches and leaves on plate 

 Ixi, figs. 12-15. The specimens figured upon this last plate are all from Dr. 

 Hayden, and, though very numerous, none of them has any trace of these 

 laciniate divisions, except the small brauchlet, fig. 15, where the thread-like 

 filaments are simple, short, and apparently representing the base and remnants 

 of leaves destroyed by maceration, an appearance also less definitely marked 

 upon the lower branches of fig. 13: per contra, the specimens sent by Mr. 

 Cleburn from the same locality have only the part of stem, plate Ixiv, fig. 13, 

 and very numerous fragments of the form, fig. 12, but no branch with leaves 

 like those described as Selaginella falcata. For this reason, and that of doubtful 

 identity, they have been described and figured separately. 

 Habitat. — Point of Rocks, Wyoming ( Wrn. Cleburn). 



