Ford.^The Anatomy of P silo turn triquetrum . 603 
groups of xylem with the somewhat irregular protoxylem, and again the 
whole appearance of the cortex with its absorptive hairs and cells with 
clearly defined fungal filaments and probable reproductive bodies, recall 
very forcibly some sections of Psilotum . As Professor Weiss has pointed 
out, it is impossible to decide the systematic position of this fossil root or 
rhizome until more is known of the whole plant to which it belongs ; too 
much stress, therefore, must not be laid on these resemblances to Psilotum , 
however strongly marked and interesting they may be. 
Summary. 
1. Psilotum possesses a much-branched aerial and subterranean stem, 
and greatly reduced leaves with no vascular supply. There are no roots. 
2. The plant is monostelic throughout. A protostele is found at the 
base of the aerial stem, and this is often succeeded by a medullated stage. 
In the aerial branches a central core of sclerenchymatous fibres is found. 
3. The protoxylem is often absent in the underground branches. The 
phloem throughout is poorly developed, though elements resembling sieve- 
tubes are present. Lignification of the phloem tissue may occur in the 
aerial stem. 
4. Owing to its saprophytic manner of life, Psilotum probably 
represents a much reduced form, which may have retained some primitive 
characters. The relationship to any of the living Lycopodiaceae is some- 
what distant, but the structure of the aerial stem shows resemblance to the 
fossil Lycopod Lepidodendron mundum , as well as to the axis of the cone 
of Lepidostrobus Brownii. On anatomical grounds, as well as on the nature 
of the sporangial structures, the Psilotaceae appear to be somewhat closely 
allied to the fossil group of the Sphenophyllales, 
In conclusion, I must add that this paper was begun at Cambridge at 
the suggestion of Mr. Seward, but was continued and completed at the 
Owens College, Manchester. To Mr. Seward, to Professor Weiss, and to 
Dr. Scott I owe my warm thanks for suggestions and advice given me 
throughout. My thanks are also due to Mr. Lynch for the material and 
information with which he has so often supplied me. 
Bibliography. 
Baker, J. G. : Handbook of the Fern Allies. London, 1887. 
Bary, A. de : Comparative Anatomy of Phanerogams and Ferns. Eng. Edit., Oxford, 1884. 
Bernatsky, J. : Beitrage zur Kenntniss der endotrophen Mykorhizen. Termeszetragzi Fiizetek. 
Budapest, 1899. 
Bertrand, C. Eg. : RecherchessurlesTmesipteridees. Archives botaniques du Nord de la France. 
Lille, 1881-3. 
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