Pteridophyten. 413 



dorsal surface of the protocorm. The question whether the protocorm 

 is a primitive organ or represents a later modification is left open 

 and it is pointed out that even in the marsh loving L. laterale in 

 which it appears to be no mere temporary organ but represents for 

 some time the plant body, it may well be merely a physioiogical 

 specialization carrying the plant over an unfavourable season. The 

 vascular tissue of the stem passed directly into the root and did 

 not enter the foot. The root appears late; in the two species with 

 protocorms, L. cernuum and L. laterale it is an irregulär extension 

 of the protocorm and it is suggested that it may have originated 

 by the irregulär growth and branching of the protocorm. In these 

 species, too, the protophylls and leaves are not ver} T different and 

 seem to pass gradually into one another. The vascular Strands of 

 the protophylls pass down into the protocorm where they end blindly. 

 In these two species the leaf traces also are aggregated in an inde- 

 finite manner in the middle of the axis; later a plerome cylinder 

 develops and leaf traces become attached indiscriminatel\ T to any 

 point of it. Xylem and phloem are intermingled and the vascular 

 tissue passes down into the upper part of the protocorm. In L. Bil- 

 lardieri, L. vohibile, L. scarioswn and presumably also in L. densutn 

 the vascular tissues of the stem develop before those of leaves or 

 roots. In the first of these species the development of the stele be- 

 gins by the formation of a crescentic group of protoxylem enclosing 

 protophloem ; in L. voliibile there is at first a central protophloem 

 group and two protoxylems. one on each side of it; in L. scariosum 

 there are from the first 3 — 5 protoxylem groups with protophloem 

 between them; in the earliest stage "figured the latter shows a ten- 

 dency to penetrate towards the centre of the circular stele. Of these 

 two types of stele found in the young plant the author holds that 

 the less definite form, in which the plerome cylinder develops later 

 and the traces are attached irregularly to any portion of it, is primi- 

 tive and that the more definite arrangement is a specialisation made 

 possible by the diminution of the number of leaves owing to the 

 adoption by the prothallus and young plant of subterranean habits. 

 The indefinite type of stele found in L. cernuum and L. laterale 

 undergoes no essential change as the plant attains the matuieform; 

 phloem and xylem remain irregularly intermingled and their posi- 

 tions relatively to one another are always changing; neither is there 

 any constant relation between the protoxylem groups of the stem 

 and the leaf traces or branches. In the cone of L laterale, however, 

 the appendages are arranged in alternating whorls of three and the 

 axial stele is consistently triarch and shows a constant relation to 

 the traces. It was also found that the definite type of young stele 

 showed two main types of further development; in both of these 

 xylem and phloem form definite bands or plates with protoxylem at 

 the extremities; these bands are characterised by considerable defi- 

 niteness though they occasionnally change in form and number 

 owing to anastomosis. In one type, the radial bänded type, the 

 xylem bands radiate from the centre, where they may be coalescent 

 and the protoxylem is situated at the peripheral extremity; these 

 radial bands are separated by radial bands of phloem. This type 

 was characteristic of L Billardieri ; in the second kind of banded 

 stele, found in L. volubile, L. scariosum and L. densum, bands of 

 xvlem separated by bands of phloem lie more or less parallel to 

 one anoth er m the dorsal region of the stele while the radial arran- 

 o-ement is preserved in the ventral region owing to the frequent 



