A study of the anatomy of recent ferns both in the adult state and in successive stages of development from the embryo has on the whole revealed “a striking parallelism[730]” between vascular and sporangial characters in leptosporangiate ferns. For a masterly treatment of our knowledge of fern anatomy from a phylogenetic point of view reference should be made to Mr Tansley’s recently published lectures: within the limits of this volume all that is possible is a brief outline of the main types of vascular structure illustrated by recent genera. [Illustration: FIG. 237. A. _Matonia pectinata_ (petiole). B. _M. pectinata_ (stem). C. _Gleichenia dicarpa_ (stem): _p_, petiole; _pp_, protophloem; position of protoxylem indicated by black dots. D. _Matonidium._ E. _Trichomanes reniforme_: _pp_, protophloem. (C, E, after Boodle; D, after Bommer.)] To Prof. Jeffrey[731] we owe the term protostele which he applied to a type of stele consisting of a central core of xylem surrounded by phloem, pericycle, and endodermis. While admitting that steles of this type may sometimes be the result of the modification of less simple forms, we may confidently regard the protostele as representing the most primitive form of vascular system. The genus _Lygodium_ affords an example of a protostelic fern; a solid column of xylem tracheae and parenchyma is completely encircled by a cylinder of phloem succeeded by a multi-layered pericycle and an endodermis of a single layer of cells. In this genus the stele is characterised by marginal groups of protoxylem; it is exarch. An almost identical type is represented by species of _Gleichenia_, but here the stele is mesarch, the protoxylem being slightly internal (fig. 237, C). _Trichomanes scandens_ (fig. 238) has an exarch protostele like that of _Lygodium_; but, as Boodle[732] has suggested, the protostelic form in this case is probably the result of modification of a collateral form of stele such as occurs in _Trichomanes reniforme_ (fig. 237, E). A second type of stele has been described in species of _Lindsaya_[733] in which the xylem includes a small group of phloem near the dorsal surface. This _Lindsaya_ type is often passed through in the development of “seedling” ferns and may be regarded as a stage in a series leading to another well-marked type, the solenostele. The solenostele[734], a hollow cylinder of xylem lined within and without by phloem, pericycle, and endodermis, occurs in several genera belonging to different families, e.g. _Dipteris_, species of _Pteris_, species of _Lindsaya_, _Polypodium_, _Jamesonia_, _Loxsoma_, _Gleichenia_ and other genera. In a smaller number of ferns the stele consists of what may be called a medullated protostele similar to the common form of stele in _Lepidodendron_: this type is found in species of _Schizaea_ and in _Platyzoma_ (fig. 239). It is important to notice that in the solenostele and as a rule in the medullated protostele when a