82 THE SAPROLEGNIACE^ OF THE UNITED STATES, 



different modes, in a given species. In Leptomilas, they are formed in basipetal suc- 

 cession, each segment of the hypha becoming in its turn a sporangium (Figs. 115- 

 117). In 8apr6legnia and Lf^ptolegnia, the new sporangium begins by the upward 

 growth of the basal Avail of the old one, which continues so that the new fills the 

 cavity of the old more or less completely (Fig. 14). It may even grow out through 

 the month of the latter for some distance. It is not uncommon to see several suc- 

 cessive sporangia thus "nested" (Fig. 15). Rarely in most species of the genus, 

 but often in 8. monilifera, according to De Bary ('88), the renewal of sporangia by 

 the third mode, now to be described, occurs. The genera Pgthiopsis, Acldya, 

 Aplianomyces, Thraustotlteca, Dictyuclms and AjJodacMya are characterized by the 

 cymose branching of their hyphsB in the production of new sporangia. Just below 

 the basal wall of the primary sporangium arises a lateral branch which, after a period 

 of growth, develops a secondary sporangium at its tip. Successive repetitions of 

 this sympodial branching on alternate sides of the apparent axis produce a scor- 

 pioid cyme, which is usually developed with more or less regularity (Fig. 10). In 

 Pythiopsis there is a more pronounced tendency to the development of a one-sided or 

 helicoid cyme (Fig. 62). Variations from pei'fect regularity are, however, the rule 

 in most forms. It often happens that a branch remains short, and forms a single 

 sporangium with a part of the axis (Fig. 10, 3). Less often a secondary sporangium 

 is formed below the primary one, as in Leptomitas. In Aplanes the sporangia are so 

 sparingly developed that the formation of secondary ones has not been observed. 

 Hartog has stated ('88) that the sporangia oi' ApJianomyces are renewed as in Sajjro- 

 legnia, but this is certainly not true for A. scaber, in which cymose branching occurs 

 (Fig. 17) ; and the same condition probably exists throughout the genus. 



The name resting sporangia has been applied to sporangium-like structures 

 which, after being cut off from their filaments, remain unchanged for a time, but 

 which may, under suitable conditions, develop and discharge their zoospores in the. 

 usual way. They are evidently sporangia arrested in their development, probably by A 



external conditions. Their simplest form is that of the ordinary sporangium, but 

 frequently they are shorter and broader, and formed in series from the hyphae. 



Chlaviydosjwres. Many of the species of So prolegniacece may produce other 

 structures beside the sj^orangia, that are organs of non-sexual propagation and may 

 be termed chlamydospores, in the sense in which Brefeld uses that term. They 

 are usually developed in scries, as swellings at the ends of the hypha? (Fig. 18), and 



