THE LYCOPODS (CLUBMOSSES) 



hand specimen of Fig. 254 /> is from Guernsey and was especially selected as an 

 abnormally large plant with a branched stock. 



The remarkably disjunct character o^ Isoetes hystrix localities makes it certain that in 

 each must be a little inbreeding community, isolated for long periods of time, and it is 



Fig. 255. Isoetes hystrix Durieu growing in cultivation to show characteristic differences of habit in 

 material from different sources. The tall left-hand plant came from Morocco, the right-hand plant 

 from the Lizard. About a quarter natural size. 



Fig. 256. Chromosomes of /joe/ej. All x 1000. a. /. /ac?/^<m L. first meiotic metaphase, in permanent 

 acetocarmine. x 1000. For explanatory diagram see Fig. 253. b. I. hystrix Durieu from the 

 Lizard, diakinesis in permanent acetocarmine. x 1000. n= 10. c. The same, showing metaphase 

 in a section, x 1000. d. Root of/, hystrix from Morocco in a section, stained with Feulgen's 

 method, to show chromosome size, x 1000. 2n=:20. 



therefore to be expected that local populations should show genetically based differences 

 of the same type as those already met with in the aquatic species, and this is undoubtedly 

 the case. A detailed comparison between the populations of Guernsey and of the Lizard 

 has not been made owing to the inaccessibility of Guernsey during the war years. At the 

 time of my visit to that island in 1939, only a token collection of live plants had been 



MFC 



257 



17 



