GROUP I. THALLOPHYTA : ALG.E. 



crown consists of five cells as in the Chareae, or by two transverse walls, 

 so that the crown consists of ten cells as in the Nitelleae. Each oogonium 

 contains a single oosphere, a nucleated mass of protoplasm containing 

 starch-granules, with a well-marked clear area, the" receptive spot, at the 

 apical end. 



At the time of fertilisation, the cells of the crown separate so as to form 

 a channel leading to the apex of the oogonium. The wall of the oogonium 

 is not ruptured, but it becomes mucilaginous. The spermatozoids enter 

 the channel and reach the apex of the oogonium; one of them makes its 

 way through the mucilaginous cell-wall, and, entering the oosphere at 

 the receptive spot, fertilises it. 



After fertilisation, the oosphere becomes 

 an oospore, surrounding itself with a 

 proper wall. The more internal walls of 

 the investing filaments become thickened, 

 and assume a dark brown colour. The 

 whole organ falls off and undergoes a 

 period of quiescence. 



On germination, the oospore does not at 

 once give rise to an ordinary Chara plant. 

 It produces, in the first instance, an em- 

 bryo, consisting of a filamentous root and 

 a shoot of limited growth. The adult 

 form is developed upon the embryo by the 

 development of a lateral growing-point at 

 the node of the embryonic shoot (see Fig. 

 151). Fresh water. 



Sub- Class III. PILEOPHYCE.E, or 

 Brown Algae. The body may consist 

 of a single cell (e.g. Diatomaceae), but 

 is generally multicellular. When 

 multicellular, it presents various de- 

 grees of morphological differentiation, 

 being usually differentiated into shoot 

 and root, and in some cases (e.g. 

 Cladostephus, Sargassum) into stem, 

 root, and leaf. 



Vegetative multiplication is com- 

 mon in the unicellular forms, in which 



it is effected by division ; in a few forms (e.g. species of Sphace- 

 laria) it is effected by means of gemmae. 



In all but the lowest forms there is a distinction between re- 

 productive and vegetative cells, the former developing into more 

 or less highly differentiated reproductive organs. 



I'iG. 161. Chara frag His (after 

 Pringsheim: x 4). Embryogeny: 

 ap apical portion of shoot of the 

 embryo ; r primary root of embryo, 

 springing from the oospore ; tr 

 adventitious roote,; I leaves, 

 amongst which lies the growing- 

 point of the adult shoot; i inter- 

 mediate cell. 



