ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 329 



large sporangia, which arise from a single cell, are scattered irregularly 

 over the leaves ; the annulus may be much reduced. 



The position of Ceratopteris amongst leptosporangiato ferns is not 

 clear; it shows stronger affinities with the Polypodiaccse than with any 

 other group, but has also well-marked affinities with the Marsiliaceje, 

 and may possibly be intermediate in position between these two orders. 



New Type of Fern-Stele.* — A. G. Tansley and R. B. Lulham de- 

 scribe a new type of fern-stele in the creeping rhizomes of species of 

 Lindsaya, and in Davallia repens. It is a monostele, showing, in cross- 

 section, a central mass of xylem, consisting of scalariform tracheids 

 intermingled with parenchyma and surrounded by a complete ring of 

 phloem, pericycle, and endodermis, as in Gleichenia and Lygodium, but 

 differing by having, in addition to the external phloem-mantle, a strand 

 of phloem completely imbedded in the xylem near the dorsal surface of 

 the latter. This internal phloem-strand consists of typical sieve-tubes 

 mixed with parenchyma and separated by a layer of similar parenchyma 

 from the surrounding xylem. This type of stele corresponds with the 

 condition found by L. du Sablon in the young stem of Pteris aquilina, 

 and a few other cases. Its great interest is, that it appears to furnish 

 a phylogenetic link, hitherto wanting in a mature stem, between the 

 protostelic and the solenostelic structure. 



Alga-like Fern-Prothallus.f— A. P. W. Thomas describes the pro- 

 thallus of an Australasian fern, Scliizsea bifida, which is quite unlike 

 the ordinary types of fern-prothalli, and strongly suggestive of an 

 Alga. It is composed of branched filaments forming a green cushion 

 which may reach £ in. to A- in. in diameter. It differs from the fila- 

 mentous prothalli known in Trichomanes, since the latter are incom- 

 pletely filamentous, the archegonia being borne on archegoniophores 

 which are masses of meristematic cells ; whereas the prothalli of 

 Scliizsea are completely filamentous archegonia, as well as antheridia, 

 being produced on filaments. The prothalli are monoecious, but male 

 and female organs occur on distinct branches. The archegonium is 

 remarkable in having a free venter, resembling in this respect the arche- 

 gonia of typical bryophytcs ; the neck, however, is short. The question 

 arises as to whether this remarkable alga-like prothallus represents a 

 primitive or secondary form. The author prefers Goebel's explana- 

 tion advanced for Trichomanes, namely that Schizsea represents even more 

 than the latter a primitive state. 



Affinities of Tmesipteris.'j: — The same author as a result of the 

 study of the variations of the synangium-bearing structure in this 

 genus, develops the idea, previously suggested by Scott, of an affinity 

 between the Psilotaceee and the extinct group Sphenophyllales. He 

 also brings evidence to show that while the whole fertile structure repre- 

 sents a single leaf, or sporophyll, the synangium, with its axis, corre- 

 sponds to a ventral sporangiophore (Scott). The variations noted are 

 of three kinds : — (1) Sporophylls with repeated dichotomy and two or 

 three synangia; (2) Sporophylls in which the synangium is raised on 

 a stalk or pedicel ; (3) Sporophylls in which the synangium is replaced 



* Ann. Bot., xvi. (1902) pp. 157-64 (10 figs.). t Tom. cit., pp. 165-70. 

 X Proc. Koy.Soc, lxix. (1902) pp. 343-50. 



