380 



BOTANY 



PART II 



mucilage of the filament and increase in number by longitudinal division. From 

 these are derived uniciliate swarm-cells, which escape from the filament and ulti- 

 mately become attached and produce new filaments. In other related Flagellates 

 also such alga -like resting stages predominate, while the motile cells serve for 

 reproduction and dispersal. Two peculiar families of small organisms found 

 in the plankton of the sea can be placed along with the Chrysomonadinae. 

 These are the Silicon 1 agellatae ( 12 ) which have perforated siliceous skeletons 

 (Fig. 306 A} and the Coccolitho- 

 phoroideae ( 12& ) which have a wall 

 composed of calcareous plates or rods 

 and reproduce by producing usually 

 four swarm -spores (306 B}. The 

 Diatomeae and the Heterocontae 

 appear to have been derived from 

 the neighbourhood of the Chryso- 

 monadinae, so that these three groups 

 might be associated together as the 

 Chrysophyta. 



The Cryptomonadinae are rather 

 more highly organised than the 

 Chrysomonadinae and differ from 

 them in the dorsiventral protoplast 

 obliquely truncated at the anterior 

 end where two cilia of unequal length 

 arise from a depressed furrow (Fig. 

 307). Chrysidella (Zooxanthella) 

 belongs to this group. They are 

 symbiotic with various marine animals 

 (Radiolariae, Actiniae, etc.), in the 



FIG. 308. Euglena gracilis. A, Form with green 

 chromatophores (ch) ; n, nucleus ; v, vacuole and 

 red eye-spot ; g, flagellum. B, Hemi-saprophytic 

 form with small green chromatophores. C, 

 Colourless saprophytic form occurring in nutrient 

 solution in absence of light. D, Resting cyst of 

 the form C ; r, red eye-spot. E, Germination of 

 the resting cyst of the form A by division into 

 four daughter cells which later escape. (A, C x 

 630 ; B x 650; D, E x 1COO. After ZUMSTEIN.) 



FIG. 307. Cryptomonas erosa. 

 (x 650. After STEIN.) 



protoplasm of the cells of which their yellow resting cells lie. From these the 

 protoplast later emerges in the form of a ciliated Flagellate. The Dinoflagellatae 

 are related to the Cryptomonadinae. Some other genera, such as Phaeocystis and 

 Phaeothamnion which form mucilaginous colonies during most of their life, may 

 also be placed here. They suggest comparison with the Brown Algae, but it is 

 doubtful whether they should be regarded as really leading to that group. 



The starting-point of the Chlorophyceae is to be looked for among the Flagellates 

 provided with green chromatophores. 



The Euglenineae ( 12c ) are an advanced group of green Flagellates. Species of 

 JZuglena (Fig. 308 A] often form a green scum on ponds. There are nearly allied 

 but colourless saprophytic forms. Euglena gracilis can indeed be changed into a 



