52 COMPARATIVE MORPHOLOGY OF FUNGI 



This process of transformation extends also to the sporiferous hyphae. 

 Just as the sporangia lose their sporangial nature and become conidia, 

 the sporiferous hyphae lose their hyphal character and become specialized 

 conidiophores, with limited function. Parallel with this development 

 goes a shifting of the relative values for classification, e.g., in the aquatic 

 forms, as the Saprolegniaceae, the structure of the sporiferous hyphae 

 plays no or only a subordinate part, while in the Peronosporaceae, 

 the form of the conidiophores becomes an important systematic 

 character. 



The gametangia are developed as antheridia and oogonia. In the 

 lower forms they arise beside and between the sporangia, and thus show 

 their homology with them. In the Saprolegniaceous Thraustotheca 

 clavata, they change to sporangia if they find no mate (Weston, 1918). 

 In the higher forms they are specialized exclusively as sexual organs; 

 in some genera, the oogonia may develop parthenogenetically in the 

 absence of antheridia. 



In internal differentiation, there are active morphogenetic forces like 

 those in the zoosporangia. Just as in the latter, the individualization 

 of the uninucleate zoospores is eventually suppressed and the whole 

 content is discharged into a germ tube, so also in the gametangia, after 

 a certain stage, a differentiation into uninucleate male and female gametes 

 is suppressed. The oogonia and antheridia remain coenocytic, the latter 

 germinating with a germ tube instead of with sperms. In the female 

 gametangia, degeneration goes still further; in them a decreasing number 

 of gamete nuclei are admitted for fertilization while the rest degenerate. 

 Around the privileged, sexual nuclei, the protoplasm collects (and this 

 is a specifically new structure for the Oomycetes, giving the group its 

 name) to egg cells (oospheres), to which one or more male cells are 

 attracted and joined by a copulation tube. The fertilized eggs develop 

 to resting spores (oospores). At germination these change into zoospor- 

 angia or germinate with germ tubes. 



As in Olpidium in the Archimycetes and in Pohjphagus in the Chytri- 

 diales, caryogamy does not coincide with plasmogamy, but occurs only 

 at the germination of the zygote, sometimes months after plasmogamy 

 has occurred. Between plasmogamy and caryogamy is inserted a 

 dicaryophase which physiologically is equivalent to the diplophase, but 

 carries the possibility of entirely new developments. We will meet it 

 again in the Zygomycetes. 



The classification rests next upon the structure of the zoospores; the 

 uniflagellate and the biflagellate groups are usually treated separately. 

 In the uniflagellate group two families may be distinguished, the Mono- 

 blepharidaceae, with hyphae smooth and undifferentiated, and the 

 Blastocladiaceae with constrictions and partial differentiation into main 

 axis and secondary shoots. Furthermore, the Monoblepharidaceae 



