THALLOPHYTA. 659 



phores and the bulk of the protoplasm move from each end. A wall is now formed 

 round the contents of this swelling. Although the behaviour of the nucleus has 

 not been followed, this certainly suggests a reduced process of conjugation, each 

 half of the cell representing a gamete. 



MougeotioiDsis is a genus whose chromatophore possesses no pyrenoids. 



Alliance X. — Charales. 

 Family : Characece, the Stone worts. 



Are green submerged plants with segmented axes bearing whorls of leaf-like 

 appendages at the nodes, upon which the antheridia and oogonia are borne. The 

 antheridia are spherical and contain a large number of filaments, each cell of which 

 produces a spermatozoid with two long cilia. The oogonium consists of an egg-cell 

 inclosed in five spirally-twisted, tubular cells; on germination the egg-cell gives 

 rise to a simple segmented filament (the pro-embryo) from which the adult form 

 arises as a lateral bud. There are no swarm-spores. Vegetative propagation is by 

 bulbils, detached branches, &c. This alliance, though placed here in sequence with 

 the other alliances of Green Algae, is probably remote from them in actual affinity. 

 The Charales form an isolated and anomalous group, and various views are enter- 

 tained as to their true position. 



Members of this group occur very commonly in ditches, ponds, &c., and in 

 brackish water. In the Norfolk Broads very extensive growths of these plants 

 occur in the muddy bottom of the Broads, the living plants resting on the decom- 

 posing remnants of former generations; in this way the bottom level is being 

 gradually raised. 



Chara fragilis (see fig. 374) is perhaps the commonest species of the group, and 

 is cosmopolitan in its distribution. The plant is some 12 inches high, and consists 

 of axis with whorled leaf -like appendages inserted at the nodes. The axis consists 

 of a number of long cells (the internodal cells) with which alternate the short 

 nodal cells. The former remain undivided, whilst the latter originate the append- 

 ages and also a number of tubes, which, growing both upwards and downwards, 

 everywhere cover in the internodal cells, forming a sort of cortex. The " leaves " 

 have a structure essentially similar to that of the stem; they are, however, of limited 

 growth (fig. 374^). They bear at their nodes tiny leaflets and the reproductive organs. 

 The oogonia and antheridia occur together in this species (figs. 374 ^ and 374^), 

 the latter below the former. The antheridia are spherical orange-coloured bodies, 

 consisting of eight shields or plates whose edges dovetail into one another; each 

 bears a process (the manubrium) on its inner surface, and each of these manubria 

 bears a tuft of filaments (fig. 374 ^), in every cell of which a coiled spermatozoid is 

 produced bearing 2 long cilia at the tip (figs. 374*^ and 374 ''). The shields now dis- 

 articulate and the spermatozoids escape. The oogonia (or amphigonia) remotely 

 resemble the archegonia of Ferns (c/. fig. 346 ^ p. 472). Each contains a big oval egg- 

 cell inclosed in a sheath of 5 tubes spirally wound around it. The tips of these tubes 



