The Lower Plants 75 



tion is in a very chaotic condition, although much is 

 being done to clear up some of the most puzzling 

 questions relating to their development and affini- 

 ties. We may for convenience's sake divide them 

 into two classes, Ascomycetes, or Sac-fungi, and 

 Basidiomycetes, which include the familiar mush- 

 rooms, puff-balls, etc. It must be confessed, how- 

 ever, that only with difficulty can a good many forms 

 be brought within these categories; and as to the 

 relation of these two groups to each other and to 

 the alga-fungi there is much difference of opinion. 



Sac-fungi, Ascomycetes Among the simpler 



sac-fungi are many species known popularly as mil- 

 dews, which are often troublesome parasites upon 

 various plants. The common rose-mildew ( Sphsero- 

 theca) is one of the best known. Another closely 

 related species, which has been carefully studied, is 

 common on the dandelion. The body of the fungus, 

 or " mycelium " as it is technically called, consists of 

 a mass of slender filaments composed of rows of 

 long cells, which form a film over the surface of the 

 leaf on which it is growing. Into the epidermal cells 

 of the leaf are sent little suckers by means of which 

 the fungus feeds, and presently it sends up upright 

 branches into the air, from which little spores are 

 cut off in rapid succession and quickly grow into 

 a new mycelium if the conditions are favorable. 



Another type of spore is produced also by most of 

 the mildews. As the result of a simple form of 

 sexual reproduction, two cells unite and the con- 



