THE ANCIENT FERNS 



Romulea columnae, are also present. On the island of Guernsey, from which my material 

 comes, Ophioglossum lusitanicum is a markedly xerothermal plant, in some ways resembling 

 in its requirements Isoetes hystrix. It is found in a few shallow hollows near the summit of 

 cliffs on the south coast of the island, which enjoy very full 

 insolation and almost complete protection from north, west 

 and east. It is not surprising, therefore, that in cultivation it 

 seems to appreciate an annual period of desiccation as does 

 /. hystrix, and, in fact, it has been given treatment exactly 

 corresponding to that described on p. 256 since 1939, when 

 it was first collected, and no plants have been lost by death 

 since that date. Owing to neglect during the war, however, 

 and to an accidental shortening of the growing season for 

 several successive years, sporangia have ceased to be pro- 

 duced. For this reason the cytological study has been less 

 complete than would otherwise have been possible. 



Sections of roots show at once what has been encountered 

 so often in the Pteridophyta, namely, that 

 the chromosomes are so numerous that 

 mitotic figures are virtually useless for 

 evaluating them. Fig. 262 c, however, 

 shows meiosis with an explanatory dia- 

 gram in Fig. 263 a. It was obtained in 

 1940 from the first crop of fronds to be 

 produced in cultivation. Though good 

 enough for an approximate count, the 

 preparation is unfortunately not quite ad- 

 equate to establish the gametic number 

 with final accuracy. The approximate 

 value is, however, unquestionably of the 

 order of w=i28, though the number of 

 cells available is too small to exclude a 

 possible margin of error of one or two 

 chromosomes. Since the difference be- 

 tween 128 and, say, 126 is of importance 

 in interpreting the whole position, as 

 anyone who has followed the description 

 of Cystopteris will understand, it is desir- 

 able not to prejudice the argument at this 

 stage by claiming a premature finality. The haploid number for Ophioglossum lusitanicum 

 must therefore for the moment remain in the uncertain position of^n = c. 128 or, more 

 precisely, 'not less than 125 nor more than 130'. Even so, the reader may feel that here 

 are quite enough chromosomes for such a tiny plant. 



0. vulgatum, the Common Adder's Tongue, is not infrequent in moist meadows near 

 Manchester, and I was fortunate in having been able to collect fairly abundant material 



263 



Fig. 261. a. Ophioglossum lusitanicum L. from a dried 

 specimen from the Guernsey locality. Natural 

 size. b. Ophioglossum vulgatum L. from York- 

 shire, from a dried specimen. Natural size. 



