DIV. i THALLOPHYTA 421 



between the cells of which the spermatozoids make their way in 

 fertilisation. At the base of the oogoniurn there are small cells 

 (JFenchingszellen) cut off from the oogonial rudiment; in Cham there 

 is one, in Nitella three such cells. These divisions correspond to the 

 first divisions in the mother cell of the male organ. The female organ 

 may thus be regarded as an oogoniophore reduced to a single 

 oogonium. 



The egg, after fertilisation, now converted into an oospore, becomes invested 

 with a thick colourless wall. The inner walls of the tubes become thickened 

 and encrusted with a deposit of calcium carbonate, while the external walls of 

 the tubes, soon after the fruit has been shed, become disintegrated. 



In the germination of the oospore the nucleus, according to OEHLKERS and 

 ERNST, divides into four, the first division being heterotypic. The enlargement 

 of the zygote opens the membrane at its summit. While three nuclei remain in 

 the ventral portion of the zygote and there degenerate, the fourth nucleus enlarges 

 and passes into the apical protrusion, which is then cut off by a cell wall. From 

 this cell by further divisions a simple filamentous young plant consisting of a 

 number of segments is produced. From the first node of this plant rhizoids are 

 developed, while at the second some simple lateral axes arise as well as one or more 

 main axes. By the further growth and branching of the latter the adult plant 

 develops. The diploid stage in the Characeae is thus limited to the oospore, the 

 plant itself being throughout haploid. 



The behaviour of Chara crinita is remarkable. According to ERNST the 

 haploid male and female individuals of this dioecious species only occur occasionally ; 

 their cells have twelve chromosomes. Diploid female plants with twenty-four 

 chromosomes are, on the other hand, widely spread. These, which appear to have 

 arisen by the crossing of Chara crinita with other species, are propagated 

 apogamously by means of diploid egg-cells. This is therefore an example of 

 apogamy and not, as was previously assumed, of parthenogeuetic development of 

 haploid egg-cells ( 48a ). 



The formation of tuber-like bodies (bulbils, starch-stars) on the lower part of 

 the axes is characteristic of some species of the Characeae. These tubers, which 

 are densely filled with starch and serve as hibernating organs of vegetative 

 reproduction, are either modified nodes with much-shortened branch whorls (e.g. in 

 Tolypellopsis stelligera, when they are star-shaped), or correspond to modified 

 rhizoids (e.g. the spherical white bulbils of Chara aspera). 



CLASS XII 

 Rhodophyeeae (Red Algae) (^ n > 28 ' 49 ' 50 ) 



The Rhodophyeeae or Florideae constitute an independent group 

 of the higher Algae, the phylogenetic origin of which is perhaps to 

 be sought among the higher Green Algae, but they also exhibit 

 connections with the Brown Algae. They are almost exclusively 

 marine, and specially characterise the lowest algal region on the 

 coasts of all oceans. A few genera (e.g. Batrachospermum, Lemanea) 

 grow in fresh- water streams. 



2 El 



