46 BRITISH CHAEOPHYTA. 



ment of the cells of the outgrowth in the Nitellese is 

 very similar. In Nitella there is however an extra 

 cell beneath the antheridium between the flask-cell 

 and the basal nodal cell. 



In some species of Nitella the reproductive organs 

 are surrounded by mucus which often envelopes the 

 whole of the younger whorls. 



This is a very highly developed organ, 

 " probably the most complex and beau- 

 tiful structure of the kind throughout the vegetable 

 kingdom. In form it is almost spherical, sometimes 

 tapering very slightly to its base. The diameter 

 ranges from about 150 ju, in the smallest monoecious 

 Nitellse to about 1200 /u in the largest dioecious Gharse. 

 The colour ranges from pale greenish-yellow to 

 brilliant orange or dull red. The wall is composed 

 of eight convex plates or shields roughly triangular 

 in outline with slightly rounded sides (Fig. 19 i, ii). The 

 four lower are really four-sided owing to the lower 

 angle being truncate to admit of the insertion of the 

 pedicel-cell, the fourth side being very short. The 

 edges of the plates are rather irregularly crenate, 

 the crenations of adjoining plates fitting in with one 

 another. The outer surface of the plates is grooved 

 owing to infoldings of the integument forming partial 

 septa. These folds radiate from near the centre of 

 the plate to the margin, corresponding with the 

 indentations of the latter. The surface between 

 the grooves is rounded and the whole plate has the 

 appearance of being exquisitely sculptured in relief. 

 The coloration of the antheridium is due to the 

 presence of a layer of chlorophyll-granules lying close 

 against the inner wall of each plate, the outer wall 

 and the main substance of the plate being hyaline. 



