12 I HALLOPHYTA 



Their methods of reproduction are somewhat similar to those of Spirogyra. 



In multiplying by division of the cells, each part of the mother-cell-wall 

 becomes the corresponding halt" of the daughter-cell-wall, the second half 

 being formed Je novo (see Fig. 6). Conjugation takes place either by the 

 formation of a canal, as in Spirogtra, the zygote, however, being formed in 

 the canal and not in either of the conjugating cells; or the contents of the 

 conjugating cells are liberated from the cells before fusion takes place. 



VII. CHARALES. 



The Stone- Worts*. 



The Characeae (Plate 2, Fig. D), both in their vegetative structure and 

 in their reproductive organs, are decidedly more complex than any other 

 green algae, and in some respects may be regarded as intermediate between 

 these and the mosses, although the relationship of the class is rather obscure. 

 The plant consists of a main axis with long internodes and short nodes ; from 

 the latter whorls of lateral branches are given off. These lateral branches may 

 be either simple or themselves branched in the same manner as the main axis. 

 In the axil of one branch of each node another branch arises which repeats 

 the characters of the main axis. Attachment to the substratum is by moans 

 of branching, root-like outgrowths from the lowest nodes, called vhizoids. 

 The growth of each axis is controlled by an apical cell, from which other cells 

 are successively cut off by means of transverse walls. Each of these is again 

 divided transversely into a lower, which develops into the long internodal 

 cell, and an upper, from which, by further divisions, a disc of nodal cells 

 is produced, as well as the lateral branches. 



The reproductive organs of the Characeae are peculiar to the family and 

 have received special names, the female organ being called the nucule and 

 the male the globule. The globule (Fig. 7 a) is spherical and consists of 

 eight shield-like structures (called shields) dovetailing into one another at 

 their edges. From the inner face of each a stalk projects nearly to the centre 

 terminating in a single cell, to this cell six others are attached, and, from each 

 of the six, four long filaments grow out, each composed of a row of about 

 two hundred cells. A single motile male cell, the sperrnatozoid, is 

 developed in each of the two hundred cells of the filament. Hence the 

 total number of spermato/.oids in a globule will be about 8 x 6 x 4 x 200 

 = nearly 40,000. The filaments, as shown in Fig. 7 c, are closely packed 

 and twisted so as completely to fill the available space inside the globule. 

 The nucule (Fig. 7 b) is ovoid and made up of a large central cell, the egg- 

 cell, densely packed with starch (Fig. J </), surrounded by five spirally wound 



* Several species are enumerated or described in a paper by Messrs H. and |. Groves: 

 "On Characeae from the Cape Peninsula collected by Major A. H. VVoi.ley-Dod," 

 Journ. Linn. Soc. Bot. Vol. 37, July 1906. 



\ it, Ihi tricuspii vac. maci/enta, N. Dregeana and Lamprothamnus alopecuroides occur 

 near Stellenbosch. M. 



