sect, i CRYPTOGAMS 337 



matophores, while the trichogyne functions as a receptive organ for the spermatia, 

 one or two of which fuse with it, and the contents, escaping through the spermatium 

 wall, pass into the carpogonium. The sperm nucleus probably in this case, just 

 as has been demonstrated by Wille for Nemalion, passes down the trichogyne and 

 fuses with the nucleus of the egg-cell. The fertilised egg does not become converted 

 directly into an oospore, but, as a result of fertilisation, numerous branching fila- 

 ments termed gonimoblasts grow out from the sides of the ventral portion of the 

 carpogonium. At the same time, by the development of outgrowths from cells at 

 the base of the carpogonium an envelope is formed about the fertile gonimoblasts. 

 The whole product of fertilisation, including the surrounding envelope, con- 

 stitutes the fructification, and is termed a cystocarp. The profusely-branched 

 gonimoblasts become swollen at the tips and give rise to spherical, uninuclear spores 

 known as carpospores, which are eventually set free from the envelope. In the 

 case of Batrachospcrmum the carpospores produce a filamentous protonema, the 

 terminal cells of which give rise to asexual unicellular spores. These spores serve 

 only for the multiplication of the protonema. Ultimately, however, one of the 

 lateral branches of the protonema develops into the sexually differentiated fila- 

 mentous thallus. The production of spores by the protonema is analogous to the 

 formation of tetraspores by other Florideac. 



The formation of the cystoearps and carpospores is much more complicated 

 in the case of other genera, but they originate in a similar manner from carpogonia 

 provided with trichogynes. 



Ohoreocolax alius, a North Sea Floridean species, described by Kuckuok, is of 

 special interest. It grows as a parasite on another red seaweed, Rhodomela sub- 

 fusca, on which it appears in the form of a small white cushion-like growth. As 

 a, result of its parasitic mode of life the formation of chromatophores has been 

 entirely suppressed, and thus in Ohoreocolax albus a true fungus-form is represented. 



Economic Uses. — Gigartina mammillosa (Fig. 260), with cone-like cystoearps 

 2-5 mm. in length, and Chondrus crispus, with oval cystoearps about 2 mm. long, 

 sunk in the thallus tetraspores. Both forms occur in the North Sea as purplish-red 

 or purplish-brown Algae ; when dried they have a light-yellow colour, and furnish 

 the official Carragheen, "Irish Moss," used in the preparation of jelly. Agar-Agar, 

 which is used for a similar purpose, is obtained from various Florideac; Gracilaria 

 lichenoides supplies the Agar of Ceylon (also called Fucus amylaceus), Eucheuma 

 spinosum the Agar of Java and Madagascar. Muscus helminthochortus, consist- 

 ing of a mixture of different marine Algae, was formerly used as a specific for worms 

 and goitre. Corallina officinalis, a calcareous species of Florideac, was at one 

 time officinal. 



Class IX 



Characeae (Stoneworts) 



The Characeae form a sharply-defined group of Thallophytes, 

 distinctly characterised by the complicated structure of their sexual 

 organs. They may originally have been derived from the Confervoideae , 

 but the process of their evolution is uncertain, as all intermediate forms 

 are lacking, while they show in their structural development a higher 

 stage of organisation than any of the existing green Algae. The 



z 



