4 THALLOPHYTA. 



DIVISION I. 



THALLOPHYTA. 



The thallus in the simplest forms is unicellular; in the majority, 

 however, it is built up of many cells, which in a few instances 

 are exactly similar ; but generally there is a division of labour, so 

 that certain cells undertake certain functions and are constructed 

 accordingly, while others have different work and corresponding 

 structure. Vessels or similar high anatomical structures are 

 seldom formed, and the markings on the cell-wall are with few 

 exceptions very simple. The Myxomycetes occupy quite an 

 isolated position ; their organs of nourishment are naked masses 

 of protoplasm (plasmodia). 



As regards the external form, the thallus may be entirely 

 without special prominences (such as branches, members), but 

 when such are present they are all essentially alike in their 

 origin and growth, that is, disregarding the hair- structures 

 which may be developed. A shoot of a Seaweed or of a Lichen, 

 etc., is essentially the same as any other part of the plant ; only 

 among the highest Algae (Characeae, certain Siphonese, Sar- 

 gassum, and certain Ked Seaweeds) do we find the same differ- 

 ences between the various external organs of the plant body as 

 between stem and leaf, so that they must be distinguished by 

 these names. 



Roots of the same structure and development as in the Seed- 

 plants are not found, but organs of attachment (rhizoids and 

 haptera) serve partly the biological functions of the root. 



SYSTEMATIC DIVISION OF THE THALLOPHYTES. To the Thallophytes 

 belong three sub-divisions Slime-Fungi, Algae, and Fungi. 

 Formerly the Thallophytes were divided into Algae, Fungi, and 

 Lichens. But this last group must be placed among the Fungi, 

 since they are really Fungi, which live symbiotically with Algae. 

 The Slime-Fungi must be separated from the true Fungi as a 

 distinct sub-division. The Algce possess a colouring substance, 

 which is generally green, brown, or red, and by means of which, 

 they are able to build up organic compounds from carbonic acid 

 and water. The Bacteria, especially, form an exception to the 

 Algas in this respect ; like the Fungi and Slime-Fungi they have 

 as a rule no such colouring material, but must have organic car- 

 bonaceous food ; these plants form no starch, and need no light 



