414 Heterosiphonales 



The genus Monocilia Gerneck, '07 [= Heterococcus Chodat, '08] should 

 have a place in the Heterotrichales. It is a small Alga with very short 

 branched filaments, the cells of which have thin walls and a few parietal 

 discoidal chromatophores. Owing to the branched character of its filaments 

 and the homogeneous nature of its thin cell- walls it is not possible to include 

 it in the Tribonemacese. It should rather be placed in another family the 

 Monociliacese. The food-reserve is oil and the zoogonidia have two unequal 

 cilia. A ' palmella-state ' has been observed in this Alga. There are two 

 described species, M. viridis Gerneck and M. flavescens Gerneck. 



Order 3. HETEROSIPHONALES. 



This order includes only the single family Botrydiacea3, in which the form 

 of the plant differs markedly from all other Algae of the Heterokontae. Each 

 individual is a rounded or pyriform ccenocyte of macroscopic size and is 

 attached to a damp substratum by means of rhizoids. Gametes have not 

 been observed, although there are several methods of asexual reproduction. 



Family Botrydiacese. 



The family includes the single genus Botrt/diuin Wallroth (1815), which 

 was first accurately investigated by Rostafinski & Woronin (77). The plants 

 consist of green pear-shaped or spherical coenocytes, about 1 to 2 mm. in 

 diameter, growing on damp mud into which they are firmly ' rooted ' by 

 a branched system of rhizoids (fig. 265 1 and 5}. Each coenocyte consists of 

 a vesicular bladder with a lining layer of cytoplasm in which are embedded 

 numerous nuclei and chromatophores. The latter are small, lenticular or 

 fusiform, and in their very young stages, Klebs ('96) states that they contain 

 ' pyrenoid-like ' bodies. The chromatophores are situated in the outer part 

 of the lining cytoplasm and in full-grown plants they are usually arranged in 

 several layers, the nuclei being internal to them. Starch is not formed. 

 The rhizoids possess protoplasmic contents and many nuclei, but normally 

 they contain no chromatophores. Wager has observed mitotic division of the 

 nuclei in the rhizoids and states that the chromatic substance appears to 

 reside wholly in the nucleolus. 



Reproduction is purely asexual and may occur in a variety of ways, 

 depending largely upon the conditions of environment, any change of 

 conditions usually resulting in a corresponding variation of the reproductive 

 process. Rostafinski & Woronin ('77) worked out the different methods 

 of asexual reproduction and the final result in every case is the production 

 either of zoogonidia or of ' cysts ' (sometimes termed ' aplanospores '), the 

 latter often becoming hypnocysts. The whole vesicular plant becomes a huge 



