558 



HUTCHINSON'S POPULAR BOTANY 



trichogyne. The basal portion contains the oosperm, and the trichogyne 

 serves as a receptive organ for the spermatium. As the spermatia drift 

 helplessly through the water, one or more become attached to the trichogyne, 

 their contents pass through the walls of both organs and reach the oosperm. 

 By a complicated process, varying in different species, there arise a number 

 of carpospores, which are enclosed in a general envelope, the whole body 

 being known as a cystocarp. Ultimately the walls of this are ruptured, 



and the carpospores thus set free 

 give rise each to a protoneme, 

 from which a thallus is developed. 

 Several other species in allied 

 genera develop similar coatings of 

 calcium carbonate, and like Coral- 

 Una were formerly regarded as of 

 animal nature. One of these, Jania 

 rubens, is shown in fig. 704 growing 

 in tufts on the stems of another 

 Seaweed. Lithothamnium encrusts 

 the walls of rock-pools, and forms 

 strong masses on limpet-shells, 

 often whilst the limpet is still oc- 

 cupying the shell. Such an ex- 

 ample is shown in fig. 703 with a 

 small plant of Corallina growing 

 upon it. When this specimen fell 

 into our hands it presented no re- 

 semblance to a limpet, though it 

 was gliding over the rock. Hali- 

 meda tuna, a large green species, 

 presents much the appearance on 

 a small scale of the Prickly Pear 

 Cactus (Opuntia\ its points being 

 broad at the top and narrowed 

 to the base. Like Corallina and 

 Lithotkamniwm, it secretes calcium 

 carbonate to such an extent that 



its dead remains form beds of limestone of considerable thickness in 

 which the forms of the joints are well preserved. The well-known 

 Carrageen (Chondrus crispus) is a member of the Rhodophycese. At 

 one time it was a fashionable food for invalids under the name of Irish 

 Moss, the prevailing fad of the medical profession of that day being that 

 anything glutinous was nourishing. Laver (Porphyra laciniata} has also 

 had and still has its advocates as a food, or at least as a sauce, when 

 pounded and stewed, or pickled in salt. Murlins (Alaria esculenta] and 



FIG. 705. Polysiphonia. 



Portion of female plant with vorticella (d) ; (a) trichogyne 

 (6) forked hair; (c) sporogone. 



