96 EVOLUTION OF PLANTS 



blances indicate any real relationship, and it is quite as 

 likely that they are signs of degeneration, the most 

 marked resemblance being the absence of division walls 

 in the hyphse. On the whole, the smuts seem to be really 

 much more nearly related to the rusts. 



We have finally to consider, among the Fungi, the 

 peculiar organisms, the yeast-plants, which are the 

 principal agents in alcoholic fermentation. They are 

 unicellular forms, the individual cells being oval in 

 shape and multiplying rapidly by the peculiar mode of 

 cell-division known as budding. They may also, 

 under special conditions, develop a number of spores by 

 internal division. The structure of the cells is ex- 

 tremely simple, and the presence of a definite nucleus is 

 still open to question. 



The relation of the yeast-fungi to the other members of 

 the group is still a matter of controversy. Some authori- 

 ties consider them to be very low organisms, having 

 some affinity with the bacteria; others, on the strength of 

 their forming spores internally, somewhat like the Asco- 

 mycetes, regard them as the lowest members of this 

 group; still others have thought that they represent a 

 permanent conidial stage of forms related to the smuts, 

 as in the latter the spores under certain conditions may 

 bud much as do the yeast-cells : that is, the yeast- 

 cells are supposed to be spores arrested in their devel- 

 opment so that they never form filaments or hyphse. 

 Which of these hypotheses is the correct one, must at 

 present be left unanswered. 



