;,6 THE FLORA OF NEBRASKA. 



1. SAPKOL-ECrXIA Nees ab Esenb. Nov. Act. Leop. XL, II., 493. 1823. 



Mycelium of stout, branched filaments: zoosporangia clavate or cylindrical, 

 terminal, furnished with an apical papilla; zoospores crowded, ovoid, 

 biciliate; oogones terminal, rarely intercalated; antherids clavulate, ter- 

 minal upon lateral branches; oospores globose. 

 Etymology: Greek oanpoQ, decayed, and teyvrj, fringe. 



Saprolegnia ferax (Gruith.) Nees ab Esenb. Kuetz. Phyc. Germ. 157. n. 2. 1815. 

 Conferva ferax Gruithuissn Nov. Act. Acad. C. L. C. N. G, X., 2, 137. 1821. 



Oogones terminal or lateral, numerous, globose, or rarely cylindrical, with a 

 conspicuously pitted wall; antherids rare or lacking; oospores globose, 

 generally numerous, 30 fi. 

 On box-elder bugs, Leptocoris trivittatus, in aquarium, Lincoln. PI. XV., Fig. 4. 



"*. DICTYUCHUS Leitg. Pringsh. Jahrb. VII., 357. 1869. 



Zoosporangia terminal, fusoid or cylindrical, later ones formed successively 



below the terminal or upon lateral branches, apparently with a reticulum 



within, formed by the cohering membranes of the encysted zoospores; 



zoospores polyedral, each escaping through its individual opening; 



oogones one to several-spored, terminal, rarely intercalated; antherids 



present. 

 Etymology: Greek 8m- wv, net, and f,t«, have. 



Dictyndms magnnsii Lindst. Syn. Saproleg. 58, PI. I., f. 1-15. 1872. 



Zoosporangia cylindrical, several at the end of a filament, one above the 

 other; dioecious; oogones terminal, globose, smooth, not pitted; an- 

 therids clavate; oospores single, about 30 fi. 



On decaying fish in hatching vats, South Bend. PI. XV., Fig. 5, a, b, c. 



Family.- PERONOSPORACEAE. * 



Mycelium abundant, composed of septate, hya'.ine threads growing through the in- 

 tercellular spaces of various plants, piercing the cell walls by means of haustoria; asexual 

 reproduction by means of conidia produced on simple or branched conidiophores, which 

 break through the stomata or rupture the epidermis; sexual reproduction by oogones 

 and antherids borne laterally upon the mycelium, resulting in the formation of dark- 

 colored, thick-walled resting spores. 



The Peronosporaceae are very closely related to the Vaucheriaceae. Indeed, the 

 stock of this family appears to have come directly from the genus Vaucheria. The 

 shape, position, and behavior of the oogone and antherid, especially the separation of 

 the contents of each into gonoplasm and periplasm, correspond closely to what occurs 

 jn Vaucheria. The difference in thallus and the formation of conidia or zoosporangia 

 is easily accounted for by the parasitic habit. 



The method of germination is very diverse. In some cases the conidia and resting 

 spores germinate directly by a filament which forms a mycelium; in others the contents 

 break up into ciliated zoospores, which, after a period of activity, come to rest, lose their 

 cilia, and grow at once into a filament. These two methods present numerous grada- 

 tions and modifications. 



These fungi grow parasitically in the subdermal tissues of various flowering plants, 

 often causing great injury to the host. Their presence is noted by the occurrence of 

 blotches of white or yellow powder scattered over the leaves and stems. 



By Frederick E. Clements. 



