330 BOTANY PART n 



the Lichens (Lichenes), which were formerly regarded as simple 

 organisms, the thallus affords an instance of a symbiosis of Algae 

 and Fungi. 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. 



The phylogenjetic connections of the fourteen classes into which 

 the Thallophyta are divided are expressed, so far as is possible, in 

 the following scheme : 



^Bacteria, Bacteria. 

 \Cyanophyceae, Blue-green Algae. 



m 3Ii/.mmycetes, Slime-Fungi. 

 'Pervlineae, Dinoflagellates. 



: Conjugates, Conjugates. 

 Diatomeae, Diatoms. 



0> 



rf 



s 



.gf 



3 



^} 



!5 

 S 



^ 



Heterocontae. 



*<' 1/1 1 trophy ceae, Green Algae. 

 tCJiaraceae, Stoneworts. 

 Rhodophyceae, Red Algae. 



Eumycetes, Fungi. 

 Phycomycetes, Algal Fungi. 

 Phaeophyceae, Brown Algae. 



The Bacteria and Cyanophyceae are among the most simply organised Thallo- 

 phyta ; they are closely connected and are often grouped together as the Schizo- 

 phyta. They occupy an isolated position in contrast to the remaining simple- 

 Thallophytes, which with greater or less probability may be derived from the 

 Flagellatae. The Flagellatae used to be (and frequently still are) placed with the 

 lowest animals. As a matter of fact they combine plant and animal characteristics, 

 and may also be regarded as the starting-point of the lower animals. The 

 Myxomycetes may also have sprung from them as a group of colourless saprophytes. 

 The Peridineae are a further-developed branch of the Flagellatae. The simplest 

 forms among the Heterocontae, the Green Algae, and the Phaeophyceae connect 

 directly with the Flagellata ; on the other hand a direct connection of the latter 

 with the Conjugatae and Diatomeae (which together form the Zygophyceae), while 

 probable, is not shown in existing forms. 



The Phycomycetes have. branched off from the main series of the Chlorophyceae. 

 The origin'of the Red Algae and the Eumycetes, which appear to have sprung from 

 a common stock, is still in doubt. The Characeae occupy a quite isolated and very 

 advanced position, and are usually regarded as the most highly developed of the 

 Green Algae. 



The Thallophytes are commonly multiplied and distributed by 

 asextially produced spores, the mode of development of which differs 

 in the several groups. In many cases the spores arise by a process 



