LYCOPSIDA 65 



and some of the mummified remains are now known to be 

 those of conifers. Some had well organized strobih ; others 

 did not. Lycopodites stockii, from the Lower Carboniferous 

 of Scotland, appears to have been heterophyllous, with its 

 leaves in whorls, and to have had a terminal cone as well as 

 scattered sporophylls among the sterile leaves. Clearly, there- 

 fore, this species was very different from the modern L. 

 selago and, in some respects, was nearer to some members 

 of the Phlegmaria subsection. 



The sporophyte of Phylloglossum Drummondii, illustrated 

 in Fig. loD, is never more than about 4 cm high and appears 

 above ground only during the winter months, when it 

 develops a few cylindrical leaves like the protophylls of 

 Lycopodium cernuum. The most robust specimens develop, 

 in addition, a single erect stem terminating in a tiny strobilus. 

 During the hot summer months, when the ground is baked 

 hard, all the aerial parts wither and the plant survives this 

 unfavourable season as a tuber. Each year a new tuber is 

 formed (sometimes two or even three) from the apex of a 

 lateral stem-like structure, which grows out and downwards. 

 This parallel with the behaviour of the protocorm of L. 

 cernuum (Fig. loT) has led to the suggestion that Phyllo- 

 glossum exhibits *neoteny', in being able to produce spor- 

 angia while still in an embryonic stage of development. 

 Whatever the truth of this, it would certainly seem that some 

 of its pecuharities are adaptations which enable it to survive 

 adverse environmental conditions as a geophyte. From the 

 morphogenetic point of view, it is possible to see the 

 tuberization as a response to a high carbon /nitrogen ratio, 

 since the prothallus is both photosynthetic and mycorrhizal. 

 Perhaps all three 'causes' may apply, for they are not in- 

 compatible with each other and merely represent different 

 'grades of causality'. 



Chromosome counts for Phylloglossum show a haploid 

 number n = about 255, with many unpaired chromosomes 

 at meiosis, suggesting a high degree of hybridization in its 

 c 



