CRYPTOGAMS 



303 



3. Mention some of the ways in which their presence may contribute 

 to the contamination of drinking water. 



4. Refer to Exp. 66, and account for the bubbles and froth that usually 

 accompany these plants in the water. 



5. Can you suggest any other causes than the evolution of oxygen that 

 might produce the same effect ? 



6. Is the presence of these gas bubbles of any use to floating plants ? 



III. FUNGI 



343. Classification.- In the fungi the thallus structure 

 is greatly modified, appearing usually as a network of fine 

 threads called the mycelium 

 (pi., mycelia), from a Greek 

 word meaning " fungus " 

 (369). These plants are 

 all, with a few doubtful 

 exceptions, parasites or 

 saprophytes which contain 

 no chlorophyll and are 

 incapable of supporting an 

 independent existence. 

 Biologists are divided as to 

 their position in the genea- 

 logical tree of life. The 

 weight of authority 

 at present inclines to 

 the view that they are 

 degenerate forms de- 

 rived from the algae, 

 but they have been 



cr^ rnrrMfif>rl Vnr thoir FIG. 432. A common form of mold, magnified, 



showing thallus modified into a fibrous mycelium : 

 parasitic habits as tO a, a, spore cases ; 6, mycelium. 



render their position 



in the general scheme of life a doubtful one. They repre- 

 sent an offshoot, or side branch, as it were, of the great 

 evolutionary line, and so may be considered for the present 

 as standing apart in a class by themselves. 



