378 BOTANY VAI:T n 



the spherical masses of carpospores, which subsequently become free, are derived 

 (Fig. 314 E). 



Harveyella mirabilis ( 47 ), one of the Florideae occurring in the North Sea, is of 

 special interest. It grows as a parasite on another ivd .seaweed, RhodomeJu xuli- 

 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 chromatophoivs Las 1 n 



entirely suppressed, and, thus this plant behaves like a true Fungus. 



Economic Uses. Giyartina mammillosa (Fig. 311), with peg-like cystocarps 

 2-5 mm. in length, and Chondrus crispus (Fig. 310), with oval cystocarps about 

 2 mm. long, sunk in the thallus, tetraspores in groups on the terminal segments 

 of the thallus. 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 Florideae : Gmciluria 

 lichenoidts supplies the Agar of Ceylon (also called Fucus amylaceus), Eucheuina 

 spinosum, the Agar of Java and Madagascar. 



CLASS XIII 

 Phyeomycetes ( 4S> 49> 50 ) 



In the nature both of their thallus and sexual organs the Phyeo- 

 mycetes exhibit a close connection with the Siphoneae. The phylo- 

 genetic origin of most of the Phyeomycetes must be sought in this 

 group, though certain forms point to a relationship with other (In-m 

 Algae (e.g. Basidiobolus with the Conjugatae). They can only for the 

 present be regarded as a definite class, pending their separation into 

 several series derived from distinct classes of Algae. 



The thallus consists of extensively branched tubular threads in 

 which, as is the case in Vaucheria, transverse septa only form in 

 connection with the reproductive organs. The continuous proto- 

 plasmic mass contains numbers of very small nuclei, but chromato- 

 phores are entirely wanting in these colourless organisms. The 

 whole thallus of a Fungus is spoken of as the mycelium, the 

 individual filaments as hyphae. In the Phyeomycetes the hyph;i- 

 are non-septate, their division into distinct cells only taking place 

 in a few cases. The plants are either saprophytes occurring on the 

 putrefying remains of animals or plants in water or on decaying 

 organic substances exposed to air, or they live parasitically in the 

 tissues of higher plants or on insects. 



Asexual reproduction is effected by means of spores. These are 

 formed in the majority of the genera within sporangia, the proto- 

 plasm of which splits into the numerous spores. The latter escape 

 in the genera which live in water as ciliated swarm-spores (Fig. 316) ; 

 in the forms which are exposed to the air the spores are enclosed in 

 a cell wall (Fig. 323). The conidia, which are sometimes found 



