PHYCOMYCETES 37 



nucleus of the mature oosphere is normally the only nucleus 

 with the double chromosome number it is usual to regard the 

 oospore as sporophytic, and since the fusion nucleus is thought 

 to undergo immediate reduction in all members of the group the 

 remainder .of the cycle is termed gametophytic. Consequently 

 forms which mature the oospore without fertilization are regarded 

 as apogamous. Oomycetes in which oospores form in the com- 

 plete absence of the antheridium are termed apandrous. 



Classification. — The taxonomic study of the fungi has engaged 

 the attention of mycologists for two hundred years. During 

 this period various systems of classification have been proposed. 

 Early students were content with any orderly arrangement of 

 genera which placed together fungi of similar morphology. 

 Modern workers have sought to provide a natural scheme of 

 classification representing phylogenetic relationships. 



At the beginning of this chapter, it has been shown that two 

 outstanding points of view exist with respect to the origin of 

 the fungi. Some students regard the group as monophyletic. 

 Others look upon it as merely an assemblage of relatively unre- 

 lated forms, which have degenerated along several different 

 lines from the algae. Until general agreement is reached as to the 

 origin of the group, it is evident that no one system of classifica- 

 tion will receive the unqualified endorsement of all authorities. 

 It is true, also, that even an admittedly excellent classification 

 has only temporary value. Investigation is constantly bringing 

 to light new facts, and these at times change points of view and 

 necessitate alteration in the content of groups and in their 

 arrangement. It is not likely that any classification will ever 

 be accepted as permanent. 



The Phycomycetes are usually treated as a unit, and constitute 

 the lowest of the three primary subdivisions (classes) into which 

 the fungi are customarily divided. The number and content 

 of the orders and families making up the Phycomycetes do not 

 differ greatly in the various well known modern separations, 

 but no two classifications are wholly alike. No one of them has 

 been accepted generally as the standard. The best known 

 treatments are those of Schroter (1892-1893) and Fischer (1892) 

 published at practically the same time nearly forty years ago. 

 Though now much out of date, they are still used by many 

 students. In the classification of Schroter the Phycomycetes 

 are separated into two sub-classes, (1) the Oomycetes, embracing 



