Class 4. HETEROKONT^:. 



THIS class has been recently established by Luther to embrace 

 a number of Algae which were for a long time regarded as members 

 of the Chlorophycese. 



They are yellow-green in colour owing to the presence of a 

 large quantity of xanthophyll in the chromatophores, and the 

 product of metabolism is an oil. 



The class was instituted to include two series of organisms, one 

 of which, the ' Chloromonadales,' is distinctly a group of the 

 Flagellata, including certain primitive Flagellate organisms from 

 which the rest of the Heterokontse have been evolved. Bohlin, 

 and also Black man and Tansley, place the genus Vaucheria in this 

 class under a third series, the ' Vaucheriales ' ; but I have preferred 

 to retain this genus in the Chlorophycese in the old family 

 VaucheriaceaB of the Siphoneae. Excluding Vaucheria and the 

 Flagellate group Chloromonadales, the rest of the Heterokontse fall 

 under the order ' Confervales ' proposed by Borzi in 1889, and they 

 are all strictly algal in organization. They are unicellular, multi- 

 cellular, or coanocytic in character, exhibiting a considerable 

 variety of form, and occurring as simple rounded unicells, long 

 multicellular filaments, or large gregarious coenocytes. The cells 

 usually contain many chromatophores (rarely only one), which are 

 discoidal in form, of a yellow-green colour, and devoid of pyrenoicls 

 and starch. In other respects the cell-structure is similar to that 

 described for the Chlorophycese. 



Multiplication by cell-division does not take place in some 

 genera. 



The usual method of asexual reproduction is by zoogonidj^a of a 

 somewhat peculiar character. They are generally ovoid or pear- 

 shaped and are furnished with two cilia. The latter have only 

 been accurately examined in a few genera and have been found 

 to be of unequal length. They are attached to one side of the 



