BOTANY PART ii 



of life (heterotrophic). There are also Algae which are not strictly 

 autotrophic but can in greater or less degree employ organic substances 

 in their metabolism ; these mixotrophic forms succeed well in impure 

 water. 'Such a method of classification, however, although possessing 

 a physiological value, has no phylogenetic significance, as it does not 

 express the natural relationships between the various groups. In 

 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 in connection with the Fungi. 



The phylogenetic 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. 



Myxomyeetes, Slime-Fungi. 

 mm^Dinoflagellatae, Dinoflagellates. 

 Diatomeae, Diatoms. 

 Conjugatae, Conjugates. 

 iHeterocontae. 



1 



Chlorophyceae, Green Algae. 



I~JL U 7 O 



1*+mRhodophyceae, Ked Algae. 



Eumycetes, Fungi. 

 Phycomycetes, Algal Fungi. 

 *Phaeophyceae, Brown Algae. 

 tCharaceae, Stone-worts. 



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 presents greater difficulty. 



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 have usually been regarded as the most highly developed 



