458 SYSTEMATIC BOTANY. 



a comparative description only will be necessary. The oogonia arise at 

 the end of short branches of the mycelium in the intercellular spaces of 

 living Phanerogams, and resemble those of the monoecious Saproiegniea 

 both in form and in being rarely interstitially situated on the mycelium. 

 The antheridium grows either on the same branch or a neighbouring one, 

 and is also similar in form to those of the monoecious forms of the pre- 

 ceding Order. The process of fertilization is carried out as in it too, only 

 that the protoplasm within the oogonium constantly contracts into one 

 globular mass. Professor de Bary records that he never found developed 

 oogonia without an antheridium, and extremely seldom such as had two. 

 The oospores germinate after a long period of rest, usually lasting through- 

 out the winter. Two forms of germination have been observed. In 

 Cystopus cand'idus the oospores burst and produce the same number of 

 zoospores as the asexual conidia (zoosporangia). In Peronospora Vale.- 

 rianeilce the oospores produce each a germ-tube which, by repeated rami- 

 fication, forms a new mycelium. The conidia also, as already stated, 

 either produce germ-tubes or zoospores according to the species. The 

 mycelium of Cystopus is provided with numerous organs called haustoria, 

 which, in the shape of small bladders, penetrate the cell-walls of the host- 

 plant and extract the nourishment for the use of the fungus. 



The well-known potato-disease is caused by a fungus belonging to this 

 family. It was, until lately, known as Peronospora infestans ; but, in a 

 recent work on the subject, Prof, de Bary considered it to have separate 

 generic characters, and it now bears the name of Phytopkthora infestans. 



Suborder 3. MTJCOBINI (fig. 1 D, p. 8). Fungi growing on organic 

 solutions, and consisting of a densely branching mycelium, with no 

 transverse septa up to the time of fructification, and bearing both 

 sexual organs and asexual sporangia. The result of the union of the 

 conjugating sexual bodies is called a zyyospore. The asexual spo- 

 rangia are here (like the similar organs in the two preceding orders) 

 functionally of equal value with the sexually produced zygospores. 



Zygospore 



Sporangia Zygospores 



Sporangia, Zygospores. Sporangia, Zygospores. 



ILLUSTRATIVE GENERA : Mucor, Mich, j Syzygites, Ehrb. j Rkizopus, 

 Ehrb. j Pilobolus, Tod. 



Structure and Life-history. The sporangia are similar in function and 

 in some degree in structure to the zoosporangia and conidia of the Sapro- 

 leynieae and Peronosporece. They appear at the end of sporangia- bearers, 

 which, up to the time of fructification, are, like the mycelium, without 

 septa. The spores contained by the sporangia germinate by means of 

 germ-tubes and form a mycelium by repeated ramification. This was for 

 long the only form of reproduction known in the Mucorini, and it is only 

 in recent times that the researches of Professor de Bary and others have 



