THE ANATOMY AND AFFINITY OF PLATYZOMA MICROPHYLLUM. 653 



xylem. As this simple leaf-trace separates from the stelar cylinder,' the stelar 

 phloem and xylem right and left of it close behind the outgoing leaf-trace. Mean- 

 while the outer endodermis is unbroken — a state which is maintained until the stelar 

 ring has been reconstituted. Only then does the arc of outer endodermis accompany- 

 ing the departing leaf-trace break its connection with the remainder of the endodermis. 

 This it does at two points right and left. An outer separate arc of endodermis is 

 thus liberated, and it accompanies the outgoing leaf-trace. Meantime the continuity 

 of the outer endodermis of the stele has been maintained by the appearance of tracts 

 of endodermis, right and left, which finally meet beneath the leaf-trace before the arc 

 of leaf-trace endodermis has become detached. Following the leaf- trace outwards, 

 its peripheral arc of endodermis is soon extended on the adaxial side, and completes 

 the enclosure, in which state the trace enters the leaf. 



The zonation recognised externally is seen anatomically to be apparent rather 

 than real. For it is found that the leaf-traces directed downwards are smaller and 

 supply the smaller vegetative leaves ; those towards the upper side of the rhizome 

 are larger and supply the larger and fertile leaves. The apparent zonation depends 

 upon the separate grouping of the larger and smaller leaves in their forward and 

 upward course. The smaller and larger leaf-traces originate from the stele in the 

 same way, and differ only in the extent to which they affect the stele on their 

 departure. This accords with the facts of abortive pinnation of the vegetative 

 leaves — an indication that they are of reduced type. The leaf-trace remains undivided 

 throughout, and the pinnation is always of extra-marginal type, except towards the 

 tip of the leaf, where a reduced condition exists. 



The sporangia are distributed solitarily upon the lower surface of the pinnae, and 

 terminally on the veins. They do not constitute definite sori. A well-developed 

 bundle ending runs to the base of each sporangium. There is no indusium, but hairs 

 are distributed along the veins and the revolute margins of the pinnae. The 

 sporangial stalk is short and consists of three rows of cells ; the head is globular and 

 lopsided. The annulus is typically oblique, but is irregular in position and in 

 constitution. The number of cells of the annulus is variable, and their succession 

 is apt to be irregular and interrupted. The annulus is always interrupted at the 

 stalk. The stomium is variable in form and position, and where the annulus is 

 almost horizontal no organised stomium is found. This indicates a transitional state. 

 Roughly, the sporangia are differentiated into two types — the larger sporangia with 

 few large spores (16, 14, and 12), the smaller with more numerous small spores (32-26). 

 In actual dimensions a large spore may be many times the size of a small spore. 



The facts above detailed would still allow of a Gleicheniaceous relation for 

 Platyzoma. But their divergence from the Gleichenia characters is so pronounced 

 that it seems quite impossible to retain a view of close affinity. The sporangial 

 characters are specially divergent, and indicate a probable derivative position for 

 Platyzoma from some Gleicheniaceous source. Meanwhile the retention of hairs and 



