THE LYCOPODS (CLUBMOSSES) 



A viviparous form in which vegetative buds replace sporangia is also known from Win- 

 dermere and no doubt from other places. 



Material kept in culture for many years and used for cytological study of root tips 

 has been as follows : 



/. echinospora, normal form from County Kerry in Ireland. 



/. lacustris, normal form from Windermere (Fig. 252) ; viviparous form from Winder- 

 mere; var. Morei from County Wicklow, Ireland, with very long leaves; form with 

 leaves intermediate in length, Wales. 



All these plants proved to be cytologically indistinguishable with more than 100 

 chromosomes in their roots. Examination of meiosis was therefore confined to material 

 from the most easily accessible wild locality, namely, the /. lacustris colonies in Winder- 

 mere. 



As in many, or perhaps all, heterosporous Pteridophyta the maturation of mega- 

 sporangia tends to precede that of microsporangia. In /, lacustris the former takes 

 place in July, but the latter, which is greatly to be preferred for cytological purposes, 

 only at the end of August. Figs. 253 and 256 a show a metaphase plate obtained at this 

 season from Windermere, and the peculiar shapes of the chromosomes already seen in 

 Lycopodium and Equisetum are again displayed. For this reason, as in the other cases, 

 accurate counting is difficult. The cell in question contains not less than 54 pairs, nor 

 more than 56, and this, unfortunately, is as near to accuracy as has so far been attained. 



The other British species, Isoetes hystrix Durieu, is both so different and so unfamiliar 

 that a word of description about it may not be out of place. This minute terrestrial 

 species has its headquarters geographically in the Mediterranean regions, where it 

 is sparingly met with in isolated small colonies, spread from the south of France to 

 North Africa, occupying sites of an extremely xerothermal character. It is confined 

 to areas which are regularly moistened with flood water in winter, during which season 

 it vegetates freely and may become totally submerged. In summer, on the other hand, 

 the sites dry out completely, and all the plants inhabiting them pass the hot season in a 

 dormant and desiccated condition, either as subterranean geophytes {Isoetes) or as seeds 

 {Juncus capitatus). The 'Isoetetalia', as these localities are called in ecological language, 

 have been studied several times on the Continent by Braun-Blanquet and his school, 

 though I am not aware of any similar study of the only two existing British sites, which 

 are in Guernsey and on the Lizard respectively. That Isoetes hystrix is present in Guern- 

 sey has been known since i860. The Lizard site, though detected a century ago, was so 

 difficult to find again that the record was disbelieved until 1933, when plants o{ Isoetes 

 were re-found there in some quantity by R. Melville of Kew whilst searching for Juncus 

 capitatus. I am indebted to Dr Melville for instructions as to how to reach the Lizard 

 site, and I have also been able to collect material from Guernsey, on both occasions the 

 season being early April, at which time the vegetative season is almost at an end and 

 meiosis of the last microspores in progress. By June all traces of the leaves have vanished 

 from above ground, but, curiously enough, in the skilful hands of Mr Ashby, Isoetes 

 hystrix from both localities proved surprisingly easy to cultivate. Intact sods containing 

 it, together with other geophytes such as Scilla verna, were lifted in 1938 and 1939 

 and transferred to small pots in the roof greenhouse of Manchester University where 



255 



