SECT. I CRYPTOGAMS 379 



As a result of its parasitic mode of life the formation of chroniatophores lias been 

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



Economic Uses. — Gigartina maviillosa (Fig. 301), with peg -like cystocarps 

 2-5 mm. in length, and Chondrus cris2ncs (Fig. 300), with oval cystocarps about 

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

 of the tliallus. 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 ; S'phacrococcus 

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

 Euchemna s'pinosum, the Agar of Java and Madagascar. Siiecies of Gelidium. the 

 Agar of Japan. 



Class XII 

 Phycomycetes (^^' ^^' ^'^) 



In the nature both of their thalkis and sexual organs the Phyco- 

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

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

 group, though certain forms point to a relationship with other Green 

 Algae {eg. Basidiobolus with the Conjugatae). They can only for the 

 present be regarded as a definite class, pending their sejjaration 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 chroniato- 

 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 Phycomycetes the hyphae 

 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 protoplasm 

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

 genera which live in water as ciliated swarm-spores (Fig. 306) ; in the 

 forms which are exposed to the air the spores are enclosed by a cell 

 wall (Fig. 313). The conidia, which are sometimes found together 

 with sporangia, in other cases alone, are also adapted for dispersal in 

 air. They arise by a jjrocess of budding and abstriction from the ends 

 of certain hyphae which are usually raised above the substratum as 

 special conidiophores. 



The sexual organs of the Phycomycetes are in manj'^ ways 



