P'siloturn flaccidum, Wall. 387 
Sykes, Miss M. G. : The Anatomy and Morphology of Tmesipteris. Annals of Botany, xxii, 
1908, p. 63. 
Tansley, A. G. : The Evolution of the Filicinean Vascular System. New Phytologist Reprint, 
Cambridge, 1908. 
Thomas, A. P. W. : The Affinities of Tmesipteris with the Sphenophyllales. Proc. Roy. Soc., 
lxix, 1902, p. 343. 
Thomas, H. H. : On a Cone of Calamostachys Binneyana (Carruthers) attached to a Leafy Shoot. 
New Phytologist, viii, 1909, p. 249. 
EXPLANATION OF PLATE XXV. 
Illustrating Mr. Stiles’s Paper on Psilotum flaccidum . 
Fig. 1 is from a photograph by W. Tams of Cambridge. 
Fig. 1. Part of aerial stem of Psilottim flaccidum. Natural size. 
Fig. 2. Transverse section of the base of the aerial stem of P. flaccidum, showing secondary 
xylem elements, x 117. 
Fig. 3. Transverse section of the stem, showing triquetrous stele. 
Fig. 4. Transverse section of triquetrous stem with hexarch xylem. In the middle of the xylem 
are some fibres, while a few parenchymatous cells also occur in the xylem. 
Fig. 5. Transverse section through the end of a xylem arm of the stele, showing very distinct 
mesarch structure, x 176. 
Fig. 6. Transverse section through a flattened branch with tetrarch stele. 
Fig. 7. Phloem in longitudinal section. 
Fig. 8. Epidermis and assimilating layer of stem in transverse section, x 160. 
Fig. 9. Transverse section showing bifurcation of tetrarch stele with leaf-trace on one side about 
to be detached, x 117. 
Fig. 10. Longitudinal section of the leaf. x 57. 
Fig. 11. Sporophyll-trace in transverse section, x 176. 
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