GROUP I. THALLOPHTTA : ALG^E. 273 



Polysiplionia fastigiata and nigrcscens) the lateral appendage is a 

 leaf, the whole or part of which goes to form the procarp ; in the 

 Corallinacese the procarps are aggregated in receptacles. 



The sexual process consists in the fusion of the protoplasmic con- 

 tents of a spermatium with those of a trichogyne. The sperina- 

 tium is brought by the water into contact with the projecting 

 trichogyne to which it adheres, the spermatium being at this 

 time covered with a cell-wall; the intervening cell- walls are 

 absorbed at the point of contact, and the protoplasm of the sper- 

 matium enters the trichogyne. 



The product of fertilisation is a fructification termed a cysto- 

 carp, consisting of a number of 

 carposporangia. The cystocarp 

 is developed either directly or 

 indirectly from the carpogonium : 

 directly, when the procarp is uni- 

 cellular ; indirectly, when it is de- 

 veloped from both carpogonial and 

 auxiliary cells : the trichogyne 

 takes no part in the development 

 of the cystocarp, being shut off by 

 a septum. 



The simplest mode of direct 

 formation of the cystocarp occurs 

 in the Bangiacese ; the cavity of the 

 carpogonium becomes chambered, 

 by the formation of cell- walls, into 

 usually eight cells, each of which 

 is a sporangium, giving rise to a 

 carpospore : only a single spore is 

 formed in the genus Erythrotrichia. 

 In other cases of direct formation 

 (e.g. Nemalion, Batrachospermum), 

 the carpogonium gives rise to a 

 number of filaments, termed oo- 

 blastema-filaments, which bear a 

 cluster of sporangia (Fig. 160). 



In the indirect formation of the cystocarp, the carpogonium 

 fuses with one or more of the auxiliary cells. In the simplest 

 case (e.g. G-igartinacese, Rhodymeniaceae), the carpogonium fuses 

 directly with the auxiliary cell (or cells), and from the latter the 



M.B. T 



FIG. 160. Sexual organs of Nemalion 

 ( x 300). A. lends of branches bearing a 

 unicellular procavp t-o, and a group of 

 antheridia s ; the trichogyne (t) of the 

 procarp has two spermatia () adhering 

 to it. B early stage in the development 

 of the cystocarp ; the fertilised carpo- 

 gonium is undergoing growth and 

 division. C nearly mature cystocarp, 

 consisting of a number of short fila- 

 ments each terminating in a carpospo- 

 rangium. The development of the 

 cystocarp is direct. 



