14 D. P. PENHALLOW 



reflection will show that such a view can hardly be entertained, and for the following 

 reasons : 



1st. In all of the masses, except the smallest and obviously immature ones, the 

 Parka discs are well rounded and distinct, showing evident maturity. 



2nd. While in any individual mass there is a certain amount of variation in the 

 contained discs, there is constancy of dimension as between the discs of the variovxs masses. 



3rd. The difference in size shown to exist between these masses is not a graduated 

 one, but, as is evident from the dimensions given, is a clearly defined one, by reason 

 of which three separate groups are recognizable. This was, in fact, recognized by 

 Mr. Eeid, who pointed out in one of his communications the presence of bodies of two 

 dimensions at least, while Mr. G-raham suggests that such a plant might have occurred in 

 a number of forms. 



It would thus seem clear that in these masses and oval bodies we must recognize 

 sporocarps containing globular sporangia (Parka discs). As to the insertion of these spor- 

 angia on the main axis, a question is raised here which it is not at all easy to decide. 

 Two at least of our specimens show a stalk to which the sporocarps are terminal, but the 

 relation is not altogether such as to establish the connection beyond reasonable doubt. 

 Mr. Eeid adopts the view of a distinct stalk, and makes his restoration of the plant accord- 

 ingly. This view is justified by comparison with Marsilia, but is not justified by com- 

 parison with Pilularia, though there is no good reason for rejecting the view that an ancient 

 PiluJaria may have had stalked sporocarps. On the other hand, it must be kept 

 in mind that these bodies appear, for the most part, quite independent of stems of any 

 kind, and even when such association does occur, as pointed out by Mr. G-raham, the 

 masses are generally lateral to and sessile upon the stems. The weight of evidence would 

 thus seem to point to the fact that these sporocarps are sessile upon horizontal stems, such as 

 are represented by the associated structures, and in this respect the plant must be regarded 

 as having affinities with Pilularia. 



This brings us to a consideration of the character and structure of the discs as spor- 

 angia. As already shown, only a few of the masses show carbonized discs which can be 

 removed. Some of these were carefully boiled out in nitric acid by Sir "William Dawson, 

 and handed to me for microscopical examination. Most of them were found to be prac- 

 tically unaltered by this treatment, and were totally opaque. A few, however, broke up 

 or had their outer covering so far removed as to render the internal structure apparent. 

 It was obvious from the outset that each disc was invested by a thick carbonaceous layer, 

 in which no structure could be detected, except when examined as an opaque object, 

 when, as Sir William Dawson has pointed out, a reticulation of the surface is to be 

 observed, similar to that which characterizes the membranes of many sporocarps of 

 modern rhizocarpian plants. Internal to this, however, the disc was observed to consist 

 of a distinct tissue, composed of rather thin-walled cells, thus giving direct proof that 

 they were not simple spores, but of the nature of sporangia. In one or two cases they 

 also appeared to contain certain rounded bodies similar to spores, at least distinct from the 

 other parts of the structure, but so involved as to leave their identity somewhat in doubt. 



A careful search through the entire material disclosed numerous detached bodies of 

 rounded or oval form, consisting of a transparent or translucent body, to which were 

 attached the carbonized remains of what I took to be an outer and highly differentiated 



