74 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in the lower regions, developed rhizoids. Some of the projections at 

 various levels on the stem gave rise to adventitious lateral branches. 

 -Some of the lateral branches, attached by a narrow base, were readily 

 detachable and probably served for vegetative propagation. Dichoto- 

 mous branching of the stem occurred sparingly. In the rhizomes and 

 stems, epidermis, outer cortex, inner cortex, and stele can be distin- 

 guished. The epidermis in the aerial stems had a thick outer wall, 

 and stomata were sparingly present. The cortex consisted of a narrow 

 outer zone, which in the aerial stems had the character of a hypoderma, 

 and a broader inner cortex. The more delicate tissue of the inner 

 •cortex had intercellular spaces and was in relation with the stomata. 

 It possibly represented the assimilating tissue. The vascular system 

 consisted throughout of a simple cylindrical stele composed of a slender 

 solid strand of tracheids with broad annular thickenings and no 

 distinction of protoxylem and metaxylem. Surrounding the xylem was 

 a zone of phloem consisting of elongated thin-walled elements. No 

 vascular strands were given off to the small projections on the stem. 

 No vascular connexion existed between the stele of a lateral branch and 

 the stele of the parent axis. In the dichotomous branching of the stem 

 the stele divided to supply the two branches. The branch bore large 

 cylindrical sporangia. The sporangium had a thick wall, and terminated 

 a stout stalk which corresponded to a small stem. The sporangium 

 •contained numerous spores which were all of one kind. The authors 

 find the plant to be allied to Fsilophyton princeps Dawson, and place 

 them in a new class, Psilophytales. A. G. 



Contributions to our Knowledge of British Palaeozoic Plants. 

 Part L, Fossil Plants from the Scottish Coal Measures. — R. Kij)ston 

 {Trans. Roy. Soc. Edinb., 1916, 51, 709-20, 3 pis. and figs.). Descrip- 

 tions and figures of the fossil species — Sphenopteris incurva (new), 

 Sphenophyllum cuneifolimn, Sigillaria elegans, S. incerta (new), S. Stri- 

 mlensis (new), Stigmaria minuta, Lagenospermum parvulum (new). 



A. G. 



Anatomy and Affinity of Platyzoma microphyllum R. Br. — John 

 McLean Thompson {Trans. Roy. Soc. Edinh., 1916, 51, 631-56,4 pis. 

 and figs.). An account of the structure of this tropical Australian fern, 

 which is notable for the heterophyllous character of its xerophytic 

 foliage. On the horizontal rhizome, zones of reduced leaves usually 

 devoid of pinnai alternate with zones of larger pinnate fertile leaves. 

 Bifurcate leaves sometimes occur. Platyzoma has always been placed 

 in the Gleicheniacese, but differs markedly in the crowding of its leaves, 

 as well as in the remarkable characters of its stele, leaf-trace and 

 sporangia. The stele is protostelic, a continuous ring without leaf -gaps ; 

 the xylem is in two zones, the inner a storage zone ; the bulky pith is 

 sclerotic and mucilaginous, and is surrounded by a continuous inner, 

 distinct from the outer, endodermis ; outside the xylem is a narrow zone 

 of phloem, a pericycle, and external endodermis. The leaf-traces issue 

 (without leaf -gap) from the outer xylem as a crescentic mass of tracheids 

 with an outer arc of phloem ; the further development of the leaf -trace 

 and the behaviour of the endodermis are described. The sporangia do 



