only H. dilatatum and H. scabrum show any departure from the one-layered condition of the lamina. Field sporelings of each of these two species were available for study. The several-layered condition of the lamina originates in the sporeling frond, at a late stage in the ontogeny of H. scabrum but much earlier in H. dilatatum, in precisely the same way as in the sporeling of Cardiomanes, viz., as a 3-layered belt of irregular width flanking the veins of the frond segments. In progressively later fronds it extends outwards until in H. dilatatum, but not invariably in H. scabrum, it reaches to the margins. In tracing still further the ontogenetic sequence in frond structure in Cardiomanes, it was found that in the entire fronds that next arise on the young rhizome a modification of the mode of segmentation of the marginal cells sets in that results in the formation of a strengthening rib around the forward part of the frond periphery. Fig. 41 shows the actual origin of this in a young frond, and Fig. 42 shows the extent to which the rib has developed by the time such a frond is fully grown. With the inception of the rib further extension in the size of the lamina is restricted to intercalary cell-divisions in the zone within the margin. The marginal rib is a prominent feature of the frond of the mature sporophyte (Fig. 43). In sterile fronds it is continuous around the lamina to its base. In fertile fronds it is present at the places where sori are absent. There is a well-defined cuticle over the rib surface, the lamina cuticle being more delicate even on old fronds. The lamina is several-layered right up to the rib, the number of layers finally becoming four by the subdivision of the central large-celled layer. The youngest fronds examined of mature sporophytes, in which the lamina was still very small, were found to possess a fairly well-formed rib. Bower states with a figure (1889, p. 344 and Fig. 51) that the “young” frond of the well-grown sporophyte of Cardiomanes has a marginal series of hemispherical segmenting cells whose segments almost immediately subdivide to form a several-layered lamina. He does not mention the marginal rib. The present writer did not observe the condition described by Bower, probably because it occurs only in the lamina while still circinnately inrolled. Such a condition would be comparable with that which is present at a much earlier stage in the ontogeny. A marginal series of this type is a characteristic feature of the Hymenophyllaceae, but is only transitory in Cardiomanes. The rib is no doubt of importance in preventing tearing of the broad lamina. It is well known that Cardiomanes can occur in more or less exposed positions, and that under dry conditions the lamina inrolls strongly from both sides. (c) The stem stele. On the short, erect primary stem of the sporeling the phyllotaxy is spiral. With the sideways curvature of the stem apex to give the horizontal rhizome the fronds become more widely spaced apart, and are borne laterally along the two sides of the rhizome, so that the latter is dorsiventral in habit.