256 The Royal Society, London. 



thostachys zeylanica, as well as a single specimen, which tbere is reason 

 to regard as the prothallus of Psilotum. As the examination of the 

 material will occupy a considerable time, it has seemed advisable to give 

 a brief description of the mode of occurrenee and external morphology 

 of the prothallus in these tbree plants, without entering into details of 

 structure or discussing the phylogenetic bearing of the facts. 



The chief gaps in our present knowledge of the gametophytes of 

 the more isolated living Pteridophyta concern the Ophioglossa- 

 ceae and Lycopodiaceae, to which groups the prothalli described 

 below belong. The prothallus of Ophioglossum pedunculosum 1 ) 

 was described by Mettenius in 1856. It was subtenanean, consisting 

 of a small tuber, from which an erect cylindrical body proceeded. On 

 the latter, which in sorne instances was obserred to reach the surface 

 and turn green, the sexual Organs were borne. The first divisions in the 

 germinating spore of 0. pendulum 2 ) are described and figured by 

 Campbell. The prothalli of two species of Botrychium are known, 

 both of which are subterranean. That of B. virginianum 3 ) is thick 

 and flattened, and in its structure and in the localisation of the sexual 

 organs on the upper surface clearly dorsiventral. The prothalli of 

 B. Lunaria,*) however, have sexual organs on all sides. In the 

 Lycopodiaceae the prothallus is well known in the heterosporus 

 forms and in Lycopodium. The sexual generation is entirely unknown 

 in the Psilotaceae and in Phy llogl o ssum. If the author is 

 correct in attributing the prothallus to be described below to 

 Psilotum, the only two isolated genera of existing Vascular Cryptogams 

 in which the gametophyte is entireiy unknown are Tmesipteris and 

 Phylloglossum. 



Ophioglossum pendulum. 



The sporophyte of this plant was, for the most part, found growing 

 on the humus collected by such epiphytic ferns as Polypodium 

 quercifolium and Asplenium nidus. A large mass of the former, 

 with the Ophioglossum growing upon it, was collected in the Barrawa 

 Forest Reserve, 5 ) near to Hauwella, in Ceylon. On the humus contained 

 in this being carefully examined prothalli of various ages were found. 

 They were distributed throughout the humus, the majority being found 

 near the bottom of this, often embedded among the ramenta which clothe 

 the rhizome. 



The very young prothalli are button-sbaped, the slightly conical 

 lower part expanding above. The basal region is brownish, the surface 

 of the upper portion a uniform dull white. The latter tint is due to 

 the close covering of puraphyses, which, at this age, extends unin- 

 terruptedly from just above the base over the whole surface of the 

 prothallus. The youngest prothalli are thus clearly radially symmetrical. 



') „Filiees Hurti Bot. Lipsiensis". p. 119. Leipzig 1856. 



2 ) „Mosses and Ferns". p. 224. London 1895. 



3 ) Jeffrey, „Trans. Cauadian Institute". 1896—97. p. 265. 



4 ) Hofmeister, „Higher Cryptogamia". p. 307. London 1862. 



5 ) I am indebted to my friend Mr. F. Lewis, who guided me to this 

 locality, for the assistance he afforded me in my eearch for the prothallus of 

 Ophioglossum and Helminthostachys. 



