K.— BOTANY. 181 



traced throughout the class, one with a single cilium (Chromulinales), 

 another with two equal cilia (Hymenomonadales), and a third with two 

 unequal cilia (Ochromonadales). Each series is represented by motile 

 unicells (e.g. Chromulina, Ochromonas), by motile colonial types (Synura, 

 Uroglena, &c.) parallel with the Volvocales among Isokontae, and by an 

 extensive development of sedentary epiphytic forms peculiar to the class 

 and provided with a wide offstanding envelope. The palmelloid type is 

 also well represented, reaching an exceptionally high differentiation in 

 Hydrurus, while the dendroid colony is here realised by the planktonic 

 Dinobryon. All of these forms are Flagellates, but within the last dozen 

 years quite a considerable number of algal members of this class have 

 been discovered on the continent, and it is clear that the Chrysomonadales 

 too have progressed in the same direction as Isokontae and Heterokontae, 

 but that here the bulk of the forms have remained flagellate and the 

 minority have become algal. 



The latter are represented in the first place by chlorococcoid types 

 like Chrysosphaera, 13 whose spherical cells contain two parietal yellowish- 

 brown chromatophores, harbour masses of leucosin, and are invested 

 by a firm cell-wall ; they reproduce by division of the protoplast with 

 the formation of two new individuals and by means of zoospores closely 

 resembling a Chromulina. There are also a considerable number of 

 filamentous forms, such as the unbranched Nematochrysis H and the 

 branched Thallochrysis, 15 reproducing by zoospores resembling an Ochro- 

 monas and Chromulina respectively. Here also, according to the most 

 recent investigations, 16 we must refer Lagerheim's Phaeothamnion, whose 

 systematic position was long doubtful. In Hansgirg's Phaeodermatium, 17 

 not uncommon attached to stones in cold streams of Central Europe, we 

 have a discoid type parallel with similar forms in other classes. It is 

 not improbable that each of the three series of motile forms previously 

 mentioned has progressed towards the filamentous stage, although at 

 present only representatives of two of them are known. That the balance 

 in the Chrysophyceae is overweighted on the side of the presumably 

 more primitive flagellate types coincides with the fact that sexuality 

 has as yet been very rarely recorded in members of this class, and is only 

 known to be isogamous. The Chrysophyceae exhibit other special 

 developments in the direction of the Ehizopoda, which are of great 

 interest, but lack of time renders their consideration impossible. Of the 

 great diversity of Chrysophyceae, now known from many parts of the 

 continent, only relatively few have so far been observed in this country, 

 and there is a wide field for research in this respect. 



The Chrysophyceae show that in an otherwise rather homogeneous 

 class the type of ciliation may be somewhat variable. Some species of 

 Ochromonas are very similar to species of Chromulina except for this one 

 feature, and the Chromulinales may well have originated from forms of 

 the Ochromonas-tyipe by suppression of the second shorter cilium. Only 



13 Pascher, Archiv f. Protislenk. lii, 1925, p. 533. 



14 Pascher, loc. cit. p. 511. 



15 Conrad, Bull. Sci. Acad. Roy. Belgique, 1920, p. 180. 



16 Pascher, loc. cU. p. 498. 



17 Pascher, loc. cit. p. 517. 



