326 STUDIES IN FOSSIL BOTANY 



than the former group. Here, as in the family 

 generally, the stem is monostelic ; the stele, however, 

 is of a rather rudimentary type, consisting of a more 

 or less cylindrical strand of solid wood, surrounded by 

 phloem, in which, in the English species (B. ramosa 

 and B. hirsuta l ), the large sieve-tubes are sometimes 

 preserved. These two forms are very similar, and 

 not always easy to distinguish, though it is possible 

 that more than two species are concerned. B. hirsuta 

 (Will.) had a small stem, about 2-3 mm. in diameter, 

 and bore spirally arranged, somewhat crowded leaves, 

 the petioles of which were at least equal to the stem in 

 diameter. In B. ramosa, where the petioles, as a rule, 

 are relatively smaller, the stem is usually larger than in 

 B. hirsuta, sometimes reaching a diameter of 5-6 mm., 

 while in the French species, B. forensis, it attains a 

 diameter of 7.5 mm., in M. Renault's specimen. In 

 all the species, the surface of the stem, and of the 

 leaves also to some extent, was clothed by filamentous 

 multicellular hairs, which, in the case of the French 

 species, had a very peculiar structure, for each cell bore 

 a ring of teeth at its distal end, giving the hair the 

 appearance of a miniature Equisetum. This peculiarity 

 proved of some importance in identifying the various 

 organs of the plant. 



The wood of the stem consists entirely of trach- 

 eides, mostly pitted, with a transition to scalariform 

 structure, especially in the smaller elements. The 

 proportion of the two kinds of tracheides is very variable 

 in different specimens, and may prove to afford specific 

 distinctions. The protoxylem is not always well 



1 Rachiopteris ra?nosa and hirsuta of Williamson. 



