52 A TEXTBOOK OF THEORETICAL BOTANY 



2. Chlorophyceae (Green Algae, containing chlorophyll only). 



3. Cyanophyceae (Blue-green Algae, containing phycocyanin in addition 



to chlorophyll). 



4. Phaeophyceae (Brown Algae, containing fucoxanthin in addition to 



chlorophyll). 

 V Bacillariophyceae (Diatoms, containing diatomin in addition to 



chlorophyll). 

 6. Rhodophyceae (Red Algae, containing phycoerythrin and phycocyanin 

 in addition to chlorophyll). 



EUGLENOPHYCEAE 



The Euglenophyceae include both green and colourless organisms. Those 

 which possess chlorophyll are able to assimilate carbon dioxide and live as 

 plants. Those which are colourless may either live as saprophytes, or 

 holozoically like animals by ingesting solid food. The Euglenophyceae were 

 formerly included in the old group known as the Flagellata which it was 

 impossible to classify collectively either as plants or animals ; but according 

 to recent methods of classification the Flagellata are split up into a number of 

 separate groups, some of which are placed in the Thallophyta, among the 

 Algae, while others form a separate group of the Protozoa among the animals. 

 In the past it was not uncommon to consider the whole group of the Flagellata 

 as members of the Protozoa, green and colourless alike, and moreover to 

 extend the scope of the group to include many unicellular and colonial 

 Chlorophyceae, a system which still survives in some quarters, though certainly 

 erroneous. 



In the Euglenophyceae there is no definite cell wall, merely a denser 

 protoplasmic surface layer, with the result that the protoplast may exhibit 

 contractile and amoeboid movements. One or more mobile appendages, the 

 flagella, arc present, and the motile condition is dominant in the life history. 

 Pulsating vacuoles are present. The organisms may live independently or 

 may unite to form colonies held together by mucilage or possessing stalked 

 investments. 



Sexual reproduction is unknown. Multiplication is by binary fission 

 as the result of a longitudinal split of the protoplast during the motile phase. 

 Many produce thick-walled resting spores. The Euglenophyceae contain the 

 single order Euglenales. We shall consider one common green example of 

 the group, FAiglena viridis. 



Euglena viridis 



This little organism is found very commonly in fresh-water ponds and 

 ditches, where it may at times occur in vast numbers producing a green 

 colouration of the whole of the water. There are, however, a number of 

 allied species, some of which occur in brackish or even in sea water. 



1 he organism (Fig. 28) consists of a single oval or fusiform protoplast 

 which often terminates in a point at the posterior end and is enclosed in a 



