654 MR JOHN M'LEAN THOMPSON ON 



the anatomical state show a greater conservatism. In fact, Platyzoma is again a 

 type somewhat anomalous in its characters. Like Cheiropleuria it shows sporangial 

 advance with a relatively primitive vegetative condition. 



DESCRIPTION OF FIGURES IN THE TEXT. 



Figs. 1-3. Diagrams of 3 sterile pinnae of Platyzoma, seen from the upper surface. They show 

 the chief variations in the sympodial venation. 



Figs. 4, 5. Diagrams of 2 sterile pinnae of Platyzoma, seen from below. They show further variations 

 in venation. The strongly revolute margins of the pinnae bear fringes of small teethdike hairs. 



Fig. 6. Diagram of a forked pinnate leaf of Platyzoma in Kew Herbarium. The leaf is attached 

 to the rhizome, and bears pinnae both above and below the point of branching. The terminal portions 

 of this leaf are damaged. 



Fig. 7. Diagram of a forked, and probably dichotomised, pinnate leaf of Platyzoma in Kew Herbarium. 

 The leaf was detached from the rhizome. It bears pinnae both above and below the point of branching. 



Fig. 8. Diagram of a perfectly dichotomised leaf of Platyzoma, taken from an herbarium specimen 

 in Glasgow University. The leaf dichotomised at a point near to its base, and no pinnae were developed 

 below the point of branching. 



Fig. 9. Diagram of a fertile pinna of Platyzoma, seen from below. The margins are very revolute. 

 The sporangia are of variable size, but are invariably inserted terminally upon the main lateral veins or 

 upon branches of these. 



Fig. 10. Bundle-ending of a vein, supplying a sporangium of Platyzoma. It consists of a conspicuous 

 group of long reticulated tracheides, and a sheath of more delicate and narrow cells which persist to 

 the tip of the bundle. 



DESCRIPTION OF FIGURES IN THE PLATES. 



Plate I. 



Fig. 1. Transverse section of the rhizome of Platyzoma. Four large leaf-traces are seen on their 

 way out through the cortex ; a fifth is being liberated from the upper surface of the stele. On the 

 right a small leaf-trace is separating from the stele, and on the left a root- trace is departing. ( x 12.) 



Fig. 2. A multicellular unbranched hair taken from the rhizome. ( x 10.) 



Fig. 3. A filiform leaf with circinate tip, and measuring about -J- inch. It was taken from the lower 

 surface of the rhizome. ( x 6.) 



Fig. 4. Transverse section of the stele of Platyzoma, showing a large leaf-trace about to be liberated 

 on the upper surface Small leaf-traces are being separated from the sides and lower surface. The 

 xylem of the stele is clearly differentiated into an outer zone of small tracheides, and an inner zone of 

 broad tracheides intermixed with many parenchymatous groups. ( x 24.) Towards the upper side of the 

 stele the inner xylem-zone is greatly reduced. 



Fig. 5. A reduced pinnate leaf, taken from the upper surface of the rhizome. It was about 1£ inch long. 

 The pinnae are variable in size, but their venation is invariably a sympodium. ( x 6.) 



Fig. 6. A photograph of the specimen of Platyzoma upon which this paper is founded. ( x £.) 



Fig. 7. A typical filiform leaf measuring about \\ inch, seen from its lower surface. ( x 6.) It is 

 differentiated into a broad basal region, a slender middle, and a bulbous terminal region. 



Fig. 8. A photograph of part of the specimen upon which this paper is founded. The heterophylly is 

 clearly shown, and the crowding and grouping of pinnate and filiform leaves is demonstrated. (Natural size.) 



Fig. y. A " redaction " leaf which measured about 1 inch. The venation of the majority of the pinnae 



