THALLOPHYTES. 13 



But all these facts are of altogether secondary importance in determining degrees 

 of affinity in the construction of a natural system of classification of Thallophytes. 

 This object can be attained only by a comparison of such morphological charac- 

 teristics as are presented in the entire course of development 1 . Before this was 

 ascertained in all the Algae which are now more accurately known, it might have 

 been thought that the form of the sexual organs and the results of the sexual act 

 would offer the simplest means of dividing Thallophytes, without consideration of the 

 presence or absence of chlorophyll, into groups which would give a clear insight into 

 their course of development. There can be no doubt that such groups, in which 

 Fungi and Algae stand side by side, must be adopted. Such a group are the 

 Schizophytes, the simplest of the Thallophytes, including the algal group of 

 Cyanophyceae and one group of Fungi the Schizomycetes. Other algal and fungal 

 groups are more isolated and their connection with the rest is still doubtful : such 

 groups are the Myxomycetes and the Diatoms. The rest of the Thallophytes form 

 two series composed of different but connected groups, one containing Algae only, the 

 other only Fungi. These two series may therefore be termed Algae and Fungi in a 

 narrower sense of the words, since they do not include all Thallophytes usually 

 comprehended under these designations. The form and mode of operation of the 

 sexual organs and the results of the sexual act are different within each of these two 

 large groups, and in members of their subdivisions. Among nearly allied species some 

 form zygospores, some oospores, and it was mentioned above that the development 

 of sporocarps in Fungi and Algae has proceeded in different directions. 



The Thallophytes will accordingly be described in the following order, but this 

 order does not coincide with their separation into equivalent groups : 



I. Myxomycetes (Slime-Fungi). 

 II. Diatomaceae (Bacillarieae). 



III. Schizophytes. 



(a.) Forms containing chlorophyll (and Phycocyan) : Cyanophyceae. 

 (<5.) Forms not containing chlorophyll : Schizomycetes (Fission-Fungi). 



IV. Algae (in the narrower sense). 



(a.) Chlorophyceae. 

 (3.) Phaeophyceae. 

 (/.) Rhodophyceae (Florideae). 



V. Fungi. 



(a.) Chytridieae. 



; (.) Ustilagineae. 



(c.) Phycomycetes. 



(d.) Ascomycetes. 



(e.) Aecidiomycetes (Uredineae). 



(_/!) Basidiomycetes. 



1 De Bary, Zur Systemalik d. Thallophyten (Bot. Zeit. 1881, No. i). 



