410 



A TEXTBOOK OF BOTANY 



[Ch. X 



only in low degree, there is one special small group, called 

 Myxobacteriacece, probably developed from Bacteria, in 

 which the colony is somewhat highly de- 

 veloped, as illustrated in the typical form 

 herewith pictured (Fig. 279). 



Class 3. Flagellata : the Flagellates 



These are minute free-swimming organ- 

 isms of fresh water, oftenest seen 

 when material from ponds is under the 

 microscope. Over 300 species are known. 



A typical form is Euglena gracilis, rep- 

 resented in Figure 280. The slender-elon- 

 gated unicellular body, free swimming by 

 aid of the terminal long flagellum, contains 

 nucleus, large chloroplasts, a vacuole which 

 is contractile, and a red pigment spot (or 

 " eye-spot'') which is sensitive to light, 

 the nucleus with toward which the Euglena ordinarily swims. 

 It reproduces by longitudinal fission, but 

 no sexual reproduction is yet known. In 

 autumn it forms a thick-walled resting 

 spore which lasts over winter and germinates 

 in the spring, each spore (in this case) 

 producing four new plants. While Euglena 

 is ordinarily independent, making its own 

 food photosynthetically, it can also exist 

 in organic solutions as a saprophyte, under 

 which condition it loses its chlorophyll. 

 The case is of interest as showing how 

 readily the saprophytic may originate from 

 the independent habit. 

 While Flagellates are typically unicellular, they often form 

 gelatinous colonies, which are either globular and free float- 

 ing, or attached and variously branched. Sometimes the 



Fig. 280. — Eu- 

 glena gracilis ; X 

 600. 



Above is an adult 

 individual, showing 

 the very thin wall 



nucleolus, the cy- 

 toplasm, the elon- 

 gated chloroplasts, 

 the crescent-shaped 

 red pigment spot 

 (black), and, just 

 above the latter, the 

 contractile vacuole. 

 The form pictured 

 is usual, but like 

 most Flagellates 

 Euglena readily 

 changes its shape 

 and that of its in- 

 terior parts. Below 

 is shown the germi- 

 nation of a resting 

 spore* (After Zum- 

 stein.) 



