62 BRITISH CHAROPHYTA. 



Lime secretion sometimes occurs in the enveloping 

 cells of this abnormal fruit. In this case the 

 imperfectly developed oogonia takes the form of an 

 opaque whitish-coloured globular body having the 

 appearance of a small granule of chalk. 



An attempt has been made to tabulate and arrange 

 in the form of a conspectus the distinctive charac- 

 teristics of the oospores and membranes of the various 

 British species. The result will be found on pp. 69-71. 



Nearly three-quarters of the Charophyta 



are monoecious and only a little more 

 phenomena. . ,. . ^ _ 



than one-quarter dioecious. Among the 



British species there are 23 of the former and 9 of 

 the latter, the numbers being made up as follows : 

 Nitellse, monoecious 8, dioecious 2 ; Charae, monoecious 

 10, dioecious 6; Tolypellae, all monoecious; the single 

 Nitellopsis dioecious ; the single Lamprothamnium 

 monoecious. In reviewing the two large genera 

 Nitella and Chara we do not find the monoecious or 

 dioecious character correlated with greater or less 

 complexity of structure. It is however noticeable 

 that in the genus Gliara it is in the triplostichous 

 section of the Diplostephange, which may be regarded 

 as the most highly developed type, that we meet 

 with the largest proportion of dioecious species. In 

 Nitella on the other hand the sections presenting both 

 the simplest and also the most complex structure have 

 the largest proportions of dioecious species, while the 

 monoecious species greatly preponderate in the inter- 

 mediate section. It is therefore difficult to advance 

 any satisfactory theory as to the lines on which the 

 more complex state of sexuality has been evolved. 



In the case of the dioecious species the plants of 

 the two sexes do not present any important distinctive 



