GROUP I. THALLOPHYTA: ALGJ! : RHODOPHYCE^. 271 



gynes, whilst others seem to have only auxiliary cells : after 

 fertilisation, the carpogonia of the central procarpia fuse with 

 each other, and with the auxiliary cells of the other procarpia, 

 forming a large cell from the periphery of which the carpo- 

 sporangia, constituting the cystocarp, are developed. 



The cell-fusions alluded to above are frequently considered to be of the nature 

 of a sexual process. For instance, in Dudresnaya coccinea, the procarp bearing 

 the trichogyne is regarded as a tricliophore, whilst the procarp which includes 

 the auxiliary cell, but has no trichogyne, is regarded as the carpogonium proper : 

 the ooblastema-filament which grows from the former and fuses with the latter, 

 is, from this point of view, a trichoplwric tube which convejs the fertilising 

 substance of the spermatium from the trichophore to the carpogonium. From 

 the point of view of the foregoing paragraphs, the fusion of carpogouial with 

 auxiliary cells is simply of nutritive importance. Though both views are tenable, 

 the latter is strongly supported by the fact that in certain forms (e.g. some 

 Gelidiaceas such as Wrangelia, Pterocladia) the ooblastema- filaments fuse with 

 vegetative cells of the body. 



In many cases the cystocarp consists merely of the cluster of 

 sporangia (e.g. Bangia, Chautransia, Callithamnion, Dudresnaya); 

 in other cases the cluster of sporangia is surrounded by a cellular 

 investment, termed the pericarp, formed by the growth of adjacent 

 sterile cells. 



Each sporangium always gives rise to a single carpospore, which 

 is set free as a somewhat spherical unciliated cell destitute of a 

 cell-wall, and germinates without any quiescent period. 



The germination of the tetragonidia and of the carpospores has 

 only been followed in a few cases. Generally speaking the spore 

 becomes elongated in form, and is attached by the more pointed 

 end which is almost colourless ; division by a transverse wall then 

 takes place ; the elongated attached cell developes into the root, 

 the other into the shoot. 



Batrachospermum and Lemanea are exceptions to the general 

 rule that the germinating carpospore gives rise directly to the adult 

 form, and afford good examples of heteroblastic embryogeny (see 

 p. 14). In Batrachospermum, the carpospore gives rise to a small 

 flattened embryo, from which there arise monosiphonous filaments ; 

 these filaments constitute what is termed the Chantransia-forni 

 which reproduces itself by means of gonidia ; from the Chantransia- 

 form, the Batrachospermum-plant springs as a lateral branch, 

 and, producing roots, becomes independent. In Lemanea the 

 course of development is essentially the same, only that the 

 Chantransia-form does not produce gonidia. 



The life-history of the Rhodophycere is generally considered to 



