THE CHAROPHYTA 381 



cell walls are composed of cellulose, though there may be also a superficial 

 layer of a more gelatinous material of unknown composition. 



The storage material is starch, except in the oospore, where oil also 

 occurs. This starch also accumulates in special storage structures, termed 

 bulbils, which consist of rounded cells of varying size which are developed 

 in clusters on the lower stem and root nodes. They are mainly developed 

 when plants are growing in fine slimy mud. 



Sexual Reproduction 



In their reproductive organs the Characeae show a high degree of 

 specialization, and the structure of these bodies is unlike anything in other 

 phvla of the Plant Kingdom. The female organ is a large oval structure 

 with an envelope of spirally arranged, bright green filaments of cells. It is 

 termed an oogonium. The male organ is also large, bright yellow or red 

 in colour, spherical in shape, and is usually termed an antheridium, though 

 some workers regard it as a multiple structure rather than a single organ. 



The sex organs are developed in pairs from the adaxial nodal cell 

 at the upper nodes of the primary lateral branches, the oogonium being 

 formed above the antheridium. They are sufficiently large to be easily seen 

 with the naked eye, especially the bright orange or red antheridium. Many 

 species are dioecious. In others the monoecious condition is complicated by 

 the development of the antheridium before the formation of the oogonium, 

 thus preventing fertilization by antherozoids of the same plant. In this 

 case the two types of sex organs usually arise from difi^erent points on the 

 lateral branches. 



The Antheridium 



The antheridium usually takes the place of the oldest secondary branch 

 at a node on a primary lateral, thus occupying an adaxial position on the 

 primary lateral. The peripheral nodal cell which is about to form an 

 antheridium cuts off one or two discoid cells at its base and becomes 

 spherical (Fig. 365). The apical cell then becomes divided into eight cells 

 grouped in an octant. Each of these cells divides into a row of three radially 

 superimposed cells, of which only the innermost cell undergoes any further 

 division. The eight external cells enlarge and are transformed into large 

 curved plates, termed shields, thus forming the wall of the antheridium 

 surrounding an internal cavity. They have curved surfaces and their 

 adjacent walls become folded, so that the joints appear as a series of sutures 

 fitting into one another, and give the appearance in longitudinal section of 

 being multicellular. As these shield cells increase in size they become filled 

 with red or yellow pigment, and thus give the characteristic colour to the 

 antheridium. The antheridium is supported on the basal cells, the upper- 

 most of which may elongate and push into the cavity of the antheridium. 



Meanwhile the middle cell of each primary segment of the octant 

 elongates, thus carrying the inner cell towards the centre of the antheridial 



