302 BOTANY 



mode of life. Such a method of classification, however, although 

 possessing a physiological value, has no phylogenetic significance, as 

 it gives no expression to the natural relationship of the Fungi to the 

 Algae, from which they have been derived. Of the ten classes previously 

 enumerated, the Schizophyta, Peridineae, and Rhodophyceae include both 

 assimilating and colourless non-assimilating forms : the Diatomeae, 

 Conjugatae Ghlorophyceae, Phaeophyceae, and Characeae contain exclusively 

 assimilating forms; the Myxomycetes and Hyphomycetes, on the con- 

 trary, include exclusively colourless and not independently assimilating 

 forms. 



By the term Algae in its restricted sense are understood only the 

 Thallophytes represented in the classes 3 to 8 ; by Fungi, only the 

 Hyphomycetes. To the ten classes of the Thallophytes may be added, 

 as Class 11, the Lichens (Lichenes), in which the thallus affords an in- 

 stance of a symbiosis of Algae and Fungi (p. 213). From a strictly 

 systematic standpoint, the Fungi and Algae composing the Lichens 

 should be classified separately, each in their own class ; but the Lichens, 

 among themselves, exhibit such a similarity in structure and mode of 

 life, that a better conception of their characteristic peculiarities is 

 obtained by their treatment as a distinct class. 



As a rule the Thallophytes are distributed and multiplied by 

 means of asexually produced spores, but with a varying mode of de- 

 velopment in the different groups ; and also, although not in all classes, 

 they exhibit a sexual mode of reproduction. This reproduction con- 

 sists, in the simplest cases, in the production of a single cell, the 

 zygospore or zygote, by the union or conjugation of two simi- 

 larly formed sexual cells or gametes. In many of the more 

 highly developed forms, however, the gametes are differentiated as 

 small male cells or spermatozoids, and as larger female cells, the egg- 

 cells or OOSPHERES. As a result of the fusion of an egg-cell and a 

 spermatozoid, an OOSPORE is produced. The first form of sexual re- 

 production or fertilisation is termed ISOGAMOUS, the second OOGAMOUS ; 

 but these are connected by intermediate forms. 



Class I 

 Myxomycetes (Slime-Fungi) 



The Myxomycetes form an independent group of lower Thallo- 

 phytes ; in certain respects they occupy an intermediate position 

 between plants and animals, and have in consequence also been termed 

 Mycetozoa or Fungus-animals. They are represented by numerous 

 species (about 50 genera), and are widely distributed over the whole 

 earth. In their vegetative condition the Slime-Fungi consist of naked 



