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VI L— A Further Contribution to the Knowledge of Platyzoma microphyllum 
R. Br. By John M‘Lean Thompson, M.A., D.Sc., Glasgow University. 
(With Seventeen Figures in the Text.) 
(MS. received July 9, 1917. Read July 9, 1917. Issued separately October 5, 1917.) 
In a previous paper on the anatomy and affinity of Platyzoma microphyllum 
B. Br. {Trans. Roy. Soc. Edin., vol. li, No. 20, 1916), the structure of a single 
herbarium specimen of this rare Australian fern, collected by Professor Baldwin 
Spencer in 1902, at Boorroololoo, N.T., was described. Attention was directed in 
particular to the remarkable heterophylly, the anomalous stelar structure, and the 
unique sporangia and spores. The facts detailed made it difficult to indicate any 
known fern with which Platyzoma could be reasonably compared. They might be 
considered to suggest a probable derivative position for Platyzoma from some 
Gleicheniaceous source ; but their divergence from the Gleichenia characters was so 
pronounced that it seemed impossible to retain a view of close affinity between 
Gleichenia and Platyzoma. 
It was deemed advisable to delay the further consideration of the systematic 
position of Platyzoma until fuller facts were secured. In particular, it was desirable 
to determine the origin of the anomalous stelar structure, and to throw light upon 
the nature of the sporangia and spores. By the courtesy of Dr Bailey of the 
Brisbane Botanic Gardens I have • now been supplied with a number of herbarium 
specimens of Platyzoma, and with materials preserved in spirit. These have 
provided important evidence as to the stelar state, and the structure of the mature 
sporangia and spores of this fern. A full account of the stelar structure will be 
given later, but in the present paper the mature sporangia and spores will be 
considered. 
It may be well to recapitulate the facts which emerged from the examination of 
the very limited materials dealt with in the first memoir. The fertile pinnae were 
ovate-orbicular in outline, and their margins were so revolute that the stomata — 
which were restricted to the lower surface — were in an almost closed chamber. The 
margins of the pinnae bore minute irregular hairs which helped to reduce the 
entrance to the chamber. The venation was a short sympodium. The sporangia 
were disposed either terminally upon the main lateral branches of the sympodium ; 
or if more than one sporangium were developed upon a branch of the sympodium, 
the distal portion of the branch was forked, and the sporangia were again terminal 
(text-fig. 1). The mature sporangia were almost sessile, and were hidden beneath 
the revolute margins of the pinnae: They were of irregular form, and their 
dehiscence was variable. The sporangia in any one pinna varied in size, but, 
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