414 Lang —On the Morphology of Cyathodium. 
The rhizoids in C. foetidissimum are of two kinds — -wider thin-walled 
ones and others which are narrower and have well-developed peg-thicken- 
ings. In C. caver narum none of the rhizoids are thickened, but some are 
narrower than others and probably correspond to the peg- rhizoids of the 
larger species. 
The ventral scales in C. foetidissimum (Fig. 4) are small lanceolate 
structures, slightly concave towards the thallus and devoid of any trace of 
purple coloration. There is no distinction of an appendage from a basal 
portion. The tip is occupied by a small glandular cell, and similar cells occur 
at intervals round the margin. More rudimentary forms, even to single 
cells bearing a glandular cell at the tip (Fig. 4 i a), were found on the bases 
of adventitious branches, and would doubtless occur on young plants. In 
C. cavernarum the ventral scales were always filamentous structures (Figs. 
26, 37). They may simply terminate in a glandular cell, but in the larger 
ones borne on the involucre similar glandular cells occur at the junctions of 
the cells of the filament (Fig. 26). A comparison of these with the flat 
scales of C. foetidissimum showed that the latter could be regarded as 
derived from the filamentous form by a process of branching, the marginal 
glandular cells indicating the tips of the united branches (cf. Figs. 4 
and 26). 
The thallus in both species consists for the greater part of its extent 
of a single basal layer of cells upon which the air-chambers are borne. In 
C. foetidissimum , however, the basal tissue in the region of the midrib is 
several cells thick (Fig. 5). In the older portions of the thallus these cells 
were usually inhabited by Fungal hyphae. In C. cavernarum there is no 
indication of a midrib in the vegetative region, but when archegonia are 
being formed the basal tissue becomes two or three cells thick. The 
stomata are simple, the large pore being surrounded by five series of narrow 
cells. In the cells of the basal layer there are only a few small plastids ; 
those in the cells of the septa between the air-chambers are larger, but full- 
sized ones are only found in the cells of the epidermis roofing over the 
chambers. This is the true assimilating tissue of the thallus, and, as Stahl 1 
first pointed out, its cells are similarly constructed to those of the protonema 
of Schistostega, although the outer wall is not convex. The chloroplasts were 
sometimes distributed through the protoplasm, but at other times they were 
grouped around the small nucleus in the convexity of the cell which projects 
into the air-chamber (Figs. 6, 7). In C. foetidissimum there are usually 
only four or five large chloroplasts in each cell ; they are smaller and more 
numerous in C. cavernarum. Between the assimilating cells, and sometimes 
in the basal layer also, smaller cells, each containing a single oil-body, were 
present in C. foetidissimum (Fig. 7). The oil-body had a protoplasmic 
limiting membrane, and fine strands passed across the cavity bounded by 
1 Stahl, loc. cit., p. 201. 
