694 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
plant the type of his genus Zygopteris under the name of Zygopteris primceva. Speci- 
mens of the same type were discovered by Professor Renault at Autun, and made the 
subject of an admirable paper which that careful observer published in the ‘ Annales 
des Sciences Naturelles,’ 5 6me serie, Bot., tome xii. M. Renault obtained what appear to 
be four species of this genus, a specimen of one of which fortunately had preserved not 
only the petioles but the central rhizome from which the petioles sprang, leaving no 
room for disputing the petiolar character of these structures. Both Mr. Butterwortii 
and Mr. Whittaker, of Oldham, placed in my hands specimens of this genus from the 
two-foot coal at a very early stage of my inquiries, and I subsequently obtained others 
from the same coal-mine. One of these closely resembles the species described by 
M. Renault under the name of Zygopteris Lacattii , and the other appears to be 
identical with his Z. bibractiensis. I have not found any of these attached to their 
primary stem. Mr. Carruthers has referred to this genus Zygopteris as being very 
closely allied to a group of fern-stems ■which he has united to form his genus Chelepteris * . 
I presume he merely means by this that, judging from the two specimens figured by 
Cotta and Renault, these plants belong to a group in which “ the persistent bases of 
the stipes permanently clothe the small vascular cylinder” ( loc . tit.), since I am not 
aware that specimens of any of our English tree ferns have yet been found retaining 
their internal structure, or that our British examples of Zygopteris have as yet been 
absolutely identified with the stem of a tree fern. 
Plate LVI. fig. 42 represents a transverse section of a petiole which, in its general 
features, closely resembles the Zygopteris Lacattii of Renault. These petioles always 
exhibit an oval section, with a major axis of about *37 in diameter. The central vas- 
cular bundle (a) is usually detached from its normal position, through the disappearance 
of the inner cortical cellular tissue more immediately surrounding it. It consists of a 
complex group of vessels of various sizes, a transverse section of which group resembles 
the letter H, but with the extremities of the vertical bars bent inwards. The vessels 
of the central or horizontal bar (a 1 ) are always the largest, most of them having a mean 
diameter of *085. Those of each of the vertical arms (a & a") are distinctly separable 
into two sets — an inner one (a) consisting of vessels resembling those of the central 
horizontal bar ( a '), but not quite so large as the latter ones are, and an outer series (a"), 
in which the vessels are very small, rarely exceeding *005, and many of them not 
having half that diameter. Those of the inner series (a) do not seem to undergo any 
material change of position, either in sections of the same stem, made at different points, 
or in those of different stems ; but it is otherwise with the smaller ones (a"). In no 
one instance have I seen those of each of the two vertical bars occupying precisely 
similar positions. Thus in fig. 42 those on the right hand (fig. 42, a") of the vascular 
group are but little removed from the vertical bar, whereas on the left hand (a 1 ) they 
are entirely detached, and appear as two broken clusters close to the inner margin of 
* “ On the Tree Ferns of the Coal-measures, and their Affinities with existing Forms,” Report of the British 
Association for the Advancement of Science for 1872, Trans. Sect. p. 98. 
