SAPROLEGNIALES 173 



B. Trunk not cj'lindrical. 



1. Trunk more or less irregularly lobed or branched, the apical 



branches slender and bearing the reproductive cells. 



5. Rhipidium, p. 180 



2. Trunk broadly club-shaped and essentially unbranched; 



reproductive cells borne over its broadened distal end on 

 short pedicels. 



6. Mindeniella, p. 180 



1. Leptomitus Agardh {Sy sterna Algarum, p. 47, 1824). 



syn. Apodija Cornu (Bull. Soc. Bot. France, 18: 53, 1871). 



This genus contains a single well known species, L. lacteus 

 (Roth.) Agardh (Fig. 64), occurring usually in waters strongly 

 polluted by organic material. In favorable locations, such as 

 the drains from sugar factories or breweries, it often forms dense 

 masses of closely felted threads covering surprisingly large areas. 



The hyphae are of somewhat smaller diameter at their tips 

 than at their point of attachment to the substratum, but are 

 essentially cylindrical. They are constricted deeply at rather 

 regular intervals, and appear consequently to be composed of 

 definite long segments. Branching occurs usually immediately 

 below the constrictions. Though actually monopodial it may 

 later appear dichotomous. 



The most characteristic feature of the species is the trans- 

 formation in basipetal succession of its hyphal segments to 

 sporangia. The terminal segment frees zoospores through a 

 terminal pore, the constriction at its base being temporarily 

 closed by a cellulin plug. Subterminal segments in turn function 

 as sporangia freeing their zoospores through the constriction 

 into the previously emptied adjacent segment from which they 

 finally reach the outside. Sometimes the subterminal sporangia 

 are provided with lateral exit papillae. Sporangia differing 

 in form from the segments do not occur. Sexual organs are 

 unknown. The zoospores are freed as in Saprolegriia, and 

 apparently, as there, are diplanetic 



2. Apodachlya Pringsheim (1883). 



The hyphae resemble those of the preceding genus, but con- 

 strictions occur at more frequent intervals. Definite pyriform 

 to broadly ovoid sporangia, considerably broader than the hyphal 

 segments, are borne terminally (Fig. 65). Secondary sporangia 

 are formed by sympodial budding as in Achlya. Rarely inter- 



