ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 469 



general degradation of the vascular system, conpled with the geophilous 

 habit, suggests that Phylloglossum has undergone considerable reduction 

 recently in descent. 3. This reduction has led to the complete suppres- 

 sion of the megaphyllous leaves, a condition comparable with that pre- 

 sented by Ophioglossvm simplex. 4. The similarity in respective habits 

 and structure of Phylloglossum and Isoetes go to support the Lycopo- 

 dinean affinities of the latter. 5. Phylloglossum, far from being a 

 primitive form, is highly specialised. 



Structure of Psilotum flaccidum.* — W. Stiles gives an account of 

 the structure of the aerial shoots of Psilotum flaccidum. He sums up 

 his results as follows : 1. The aerial shoots differ from those of 

 P. triquetrum in being rounded .below, triquetrous above, and then 

 flattened. In the triquetrous part branches are produced in planes suc- 

 cessively at right angles ; in the flattened part branching is all in one 

 plane. A leaf is constantly associated with stem bifurcation. 2. The 

 stem-stele is band-shaped at base, triquetrous above. In the triquetrous 

 stem the xylem is hexarch, changing to tetrarch in the flattened part. 

 3. The leaves often receive a vascular supply, and when this is the case 

 with a leaf below the stem-fork, the leaf -trace is given off so that one 

 branch of the stele is practically in the axle of the leaf-trace. 4. 

 Secondary thickening is similar to that in P. triquetrum . 5. Mesarch 

 structure occurs occasionally in the lower part of the aerial stem, some- 

 times in connexion with the leaf-traces. 6. The sporangiophore-trace 

 arises like the leaf, and is continued into the sporangiophore, and ter- 

 minates in the central tissue between the three confluent sporangia, being 

 thus similar in position to the median bundle in the synangium of 

 Tmesipteris. 7. The sporophyll is probably homologous with a foliage 

 leaf ; but whether the sporangiophore is foliar in nature or is an organ 

 sui generis is uncertain. 8. The Psilotales are probably allied to the 

 Sphenophyllales and Lycopodiales, but show greater resemblances to the 

 former. 



Phylogeny of the Filicales. I. Plagiogyria. f—F. 0. Bower begins 

 a series of studies in the phylogeny of the Filicales by the publication of 

 a paper on Plagiogyria, which was proposed as a separate genus by 

 Mettenius in 1858, but has been treated by many as a sub-genus of 

 Lomaria. Bower gives a detailed account of its structure, derived from 

 a study of the West Indian species, Plagiogyria semicordata, and the 

 East Indian P. pyniophylla and P. glauca ; and compares it with other 

 ferns. His conclusions are : 1. Plagiogyria is a quite distinct genus. 

 2. It shows its relatively primitive character in the stelar structure, the 

 undivided leaf-trace, the simple forked venation, occasional dichotomy 

 of the axis, the absence of flattened scales, absence of a " true " indusium, 

 the sorus initially simple but later showing mixed character, the segmen- 

 tation of sporangium, its thick stalk, oblique annulus, and indeterminate 

 stomium, and the tetrahedral spores. ;-;. It approaches all the great 

 series of the Simplices, without showing close affinity to any one of them. 



4. It may be regarded as the most primitive type of the Bterideas. 



5. Its " mixed " character of sorus, without any indication of a gradate 



* Ann. Bot., xxiv. (1910) pp. 373-387 (pi.), 

 t Tom. cit., pp. 423-450 (2 pis.). 



