428 BOTANY PART n 



Eucheuma spinosum the Agar of Java and Madagascar, Gelidium corneum and 

 Gr, cartilagineum the Agar of Japan. 



CLASS XIII 

 Phyeomyeetes (* " 52 > 53 ' 60 ) 



In the structure both of their thallus and sexual organs the Phyeomyeetes exhibit 

 a close connection with the Siphoneae. The phylogenetic origin of most of the 

 Phyeomyeetes is probably to be sought in this group, though certain forms point 

 to a relationship with other Green Algae (e.g. Basidiobolus with the Conjugatae, 

 and the Chytridiaceae with Protococcales and Flagellata). They can only for the 

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

 derived from distinct classes of Algae. 



In the simplest cases, as in the Chytridiaceae, the thallus consists 

 of a single cell which in its young stages is a naked protoplast. 

 In the higher forms the thallus consists of extensively -branched 

 tubular threads in which, as is the case in Faucheria, transverse septa 

 only form in connection with the reproductive organs. The con- 

 tinuous protoplasmic mass contains numbers of very small nuclei, but 

 chromatophores are entirely wanting in these colourless organisms. 

 The whole thallus of a fungus is spoken of as the MYCELUIM, the 

 individual filaments as HYPHAE. In the Phyeomyeetes 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 of 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. 371) ; in the 

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

 wall (Fig. 377). The conidia, which are sometimes found together 

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

 air. They arise by a process 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 Phyeomyeetes are in many ways 

 peculiar, and the two groups of the Oomycetes and the Zygomycetes 

 are distinguished according to their nature. In the Oomycetes, 

 which stand nearest to the Siphoneae, oogonia and antheridia are 

 found ; the contents of the latter enter the oogonium by means of a 

 tubular outgrowth, and after fertilisation oospores are formed. In 

 Monoblepharis alone free spermatozoids are found. The sexual 

 organs of the Zygomycetes are alike, and on conjugation a zygospore 



