The Present Position of Palaeozoic Botany. 



169 



which the sporangium is seated corresponds to the base of the vege- 

 tative leaf (Maslen, 1898 & 1899). The sporangium, often of very 

 large dimensions compared with that of a recent Lycopod, commonly 

 has a palisade-like outer wall. It 

 is almost certain that all Lepido- 

 sfrohi were heterosporous, the mi- 

 crospurangia and megasporangia 

 being sometimes produced on sepa- 

 rate cones, sometimes on ditterent 

 parts of the same cone, as in recent 

 Sélagineïlae. The latter, for example, 

 was the case in the cone of Lepi- 

 dodendron VeWwimianum, where the 

 megasporangia occupy the lower 

 part, just as in the recent genus 

 (Fig. 9). In other cases a cone, 

 apparently complete, has been found 

 to bear microsporaugia only. 



The microspores are very small 

 (as little as 20 ft in diameter) of 

 tetrahedral form, and present in im- 

 mense numbers in each sporangium. 

 The megaspores are of relatively 

 great size (often 1 or even 2 mm 



in diameter) tetrahedral, like the microspores, in shape, and only 

 present in small numbers, sometimes 8 or even 4, in the sporangium. 

 Megaspores, usually isolated, are extremely common in the petrified 

 material of the English Coal-Measures; in certain species their Avail 

 is clothed with bristles, among which microspores are commonly found 

 entangled. At a point corresponding to the apex of the tetrahedron 

 the megaspore, in most cases, opened by flaps, often highly developed, 

 forming a passage, through which, presumably, fertilization was efifect- 

 ed. The newly discovered megaspores of Lepidostrobus foliaceus, of 

 which not more than 4 appear to have been produced in a sporangium, 

 possessed a curious episporic appendage, suggesting the so-called 

 "swimming apparatus"' of AzolJa}) The prothallus within the mega- 

 spore of Lepidostrobi is occasionally found preserved, and the arche- 

 gonia have even been recognized. 



An undescribed Lycopodiaceous fructification from the English 

 Lower Coal-Measures, provisionally named Mazocarpon, is remarkable 

 for the fact that the large, sausage-shaped megaspores are imbedded 

 in a solid parenchymatous tissue which occupies the interior of the 



Fig. 9. Lepidostrobus. Diagram of 

 heterosporous cone, in radial section. 

 ax, axis ; spli, sporophylls ; sm, sporangia, 

 seated singly on the upper surface of 

 each sporophyll; Ig, ligules; the micro- 

 sporaugia, in upper part of cone, contain 

 numerous microspores, while the mega- 

 sporangia helow are shown containing 

 4 megaspores each. 



^) R. Scott. New Phytologist. June 1906. 



