CH. X] 



THE BROWN AIXLE 



439 



of sex, invisible structurally. A common form is the Pilo- 

 bolus or Squirting Fungus (Fig. 305), which hurls its sporangia 

 towards the light, and exhibits other phenomena, which make 

 it of interest in physiological laboratories. To this group 

 belong also some forms which attack living insects (Ento- 

 morphales), familiar in Empusa muscorum which kills the 

 common House Fly ; and it is the white sporangia shot from 

 the hyphae of the fungus which 

 one can often see as a circle or 

 halo around dead flies on win- 

 dow panes. Various members 

 of this group exhibit stages in 

 the degeneration of the sexual 

 apparatus, thus illustrating 

 well a principle, amply mani- 

 fest in other groups, that the 

 parasitic habit is usually ac- 

 companied by a disuse and 

 ultimate disappearance of 

 ordinary sexual reproduction. 

 About 180 species are known. 

 Ecologically the Phycomy- 

 cetes are thus typical hystero- 

 phytes, partly hydrophytic 

 and partly aerophytic. Phylogenetically their reproduction, 

 both oosporic and zygosporic, relates them clearly to the 

 Green Algae, while the structure of their bodies brings most 

 of them close to the Siphonales (Fig. 275). 



FIG. 305. Pilobolus crystallinus, 

 grown in a moist chamber darkened 

 except for a lateral window. The 

 sporophores both bend, and project 

 their sporangia, photo tropically 

 towards the light. (From Stras- 

 burger.) 



CLASS 7. PH^BOPHYCE^ : THE BROWN 



These are the largest and most prominent of Algae, in- 

 cluding as they do the Rock Weeds, which cover all stony 

 sea beaches between the tide marks, and the gigantic half- 

 floating Kelps, which live just below. Their color is brown, 

 or golden brown, from the presence of a special pigment, called 

 FUCOXANTHIN, which occurs in their plastids with the chloro- 



