58 LYCOPODIALES [CH. 



suggested that this outgrowth may be comparable with the 

 integument which grows up from the sporophyll in the fossil 

 genus Lepidocarpon^ and almost completely encloses the 

 sporangium. In the drawings given by Miss Lyon no features 

 are recognisable which aiford a parallel to the integument 

 of Lepidocarpon. I have, however, endeavoured to show, by a 

 brief reference to this author's interesting account of the two 

 Californian species, that the physiological and morphological 

 resemblances between the megasporangia of Selaginella and the 

 integumented ovules of the seed-bearing plants are sufficiently 

 close to enable us to recognise possible lines of advance towards 

 the development of the true seed. 



Professor Campbell^ records an additional example of a 

 Selaginella — probably 8. Bigelovii — from the dry region of 

 Southern California in which the spores become completely 

 dried up after the embryo has attained some size, remaining in 

 that state until the more favourable conditions succeeding the 

 dry season induce renewed activity. 



Isoetaceae. 



The genus Isoetes is peculiar among Pteridophytes both in 

 habit and in anatomical features. In its short and relatively 

 thick tuberous stem, terminating in a crowded rosette of 

 subulate leaves like those of Juncus and bearing numerous 

 adventitious roots, Isoetes presents an appearance similar to 

 that of many monocotyledonous plants. The habit of the 

 genus is well represented by such species as Isoetes laciistris 

 and /. echinospora^ (fig. 132) both of which grow in freshwater 

 lakes in Britain and in other north European countries. 

 The latter species bears leaves reaching a length of 18 cm. 

 The resemblance in habit between this isolated member of 

 the Pteridophytes and certain Flowering plants, although in 

 itself of no morphological significance, is consistent with the 

 view expressed by Campbell that Isoetes may be directly related 

 to the Monocotyledons'*. 



1 See p. 271. 2 Campbell (05) p. 522. 



3 Motelay and VendrySs (82). « Campbell (05) p. 561. 



