Bower.—Studies in the Phytogeny of the Filicales. 437 
The apparent merging of the leaf into the stolon seen in some of 
the cases in Plagiogyria may be compared with the transitions from leaf to 
stolon described by Goebel in certain species of Utricidaria (‘Organography,’ 
Engl, ed., vol. ii, p. 240). He states that ‘ we find all transitions between 
foliage leaves and stolons, for instance in Utricidaria longifolia , U. bryopliila , 
U. coerulea, and others’. The stolons of Plagiogyria seem similarly to 
fluctuate between the two types of structure, but here it is a matter of 
balance between the leaf-primordium and the stolon-primordium, and the 
resultant structure seems to take the character of the more prominent 
partner. 
From the description thus given of the vascular structure at the base 
of the stolon in P. pycnophylla , it appears that there may be a short basal 
region which is technically protostelic ; this is followed by a region which 
is solenostelic with leaf-gaps at intervals, a structure which is characteristic 
of the lower part with long internodes ; it is succeeded by a dictyostelic 
region, where the leaves are more closely disposed and the leaf-gaps over¬ 
lap, this being the condition of the mature stock. Similar results were 
obtained from P. glanca ; the bases of the stolons were there found to 
be clearly protostelic, but the stele widened out rapidly to the soleno¬ 
stelic and dictyostelic state, the stolons in the material available being 
short, and expanding at once into leafy buds. These observations are 
of interest in showing the primitive vascular condition of the stolons at 
their base, which has its special bearing where, as in Plagiogyria , the adult 
structure is not far removed from solenostely. 
The structure of the root is diarch, and calls for no special remark. 
It has been pointed out elsewhere (‘ Land Flora,’ p. 659) that in 
Eusporangiate types the segmentation of the apex of the stem, root, leaf, 
and of the wings of the leaf, is more complex than that seen in the 
Leptosporangiate Ferns, and that this is shared in some degree by the 
Osmundaceae ; in fact that there is some accord between the segmentation 
of the sporangium and that seen in the embryonic condition of the tissues 
of the several vegetative parts. It becomes then an interesting question to 
see what is the state in Plagiogyria , a genus in which some analogy has been 
recognized with the Osmundaceae. 
It may be said briefly, and without entering into unnecessary detail, 
that the segmentation of stem, leaf, and root of Plagiogyria has not been 
found to depart from the usual Leptosporangiate type; the wings of the 
leaf also show the usual marginal series, with a regular segmentation 
(Fig. 14), a condition shared by all other Leptosporangiate Ferns, as far as 
is known, with the exception of the Osmundaceae, which latter occupy 
a peculiar primitive position. 
