86 



EVOLUTION OF PLANTS 



(Mucorini) may have originated from algae like the 

 Conjugates, just as the water-moulds are supposed to 



have originated 

 from green forms 

 resembling Vau- 

 cheria ; but the 

 structure of the 

 thallus and the 

 non-sexual spores 

 of the black- 

 moulds are so 

 very different 

 from those of the 

 Conjugates that it 

 seems much more 

 likely that the 

 similarity in the 

 sexual cells is 

 purely accidental. 

 At any rate these fungi and their near relatives the 

 insect-fungi (Entomophthoracese) must be regarded as 

 much further removed from the algae than the water- 

 moulds and white-rusts with their ciliated zoospores, and 

 distinct oogonia and antheridia. 



FIG. 22 (Phycomycetes). A, a plant of a com- 

 mon black-mould (Macor stolonifer) , with 

 groups of stalked sporangia, sp, arising from 

 the creeping filament; ;% rhizoids, or root- 

 lets; B, young; C, mature sporangium seen 

 in optical section, showing the columella, 

 col.; D-F, successive stages in the develop- 

 ment of the sexual spore or zygospore. 



THE MYCOMYCETES 



Most of the Fungi differ in structure so widely from 

 the green plants that it is difficult to find any points of 

 resemblance. These typical Fungi or Mycomycetes 

 differ in nearly all respects from other plants, both in 

 their structure and their methods of reproduction. 



