A NEW SPECIES OF THRAUSTOTHECA 

 By W. C. CoKER and J. N. Couch 



Thraiistotheca achlyoides n. sp. 



Plate 8 



Growth very vigorous but slow, the largest threads sometimes 

 reaching a diameter of 150/i, near the base, long, straight or sinuous, 

 rarely or not at all branched. Sporangia formed as in Achlya or 

 8aprolegnia, of equal or greater diameter than the threads which 

 bear them, not tapering, but often of irregular thickness throughout 

 their length, the tips rounded; the early sporangia straight or with 

 slightly curved tips, the later ones almost invariably with recurved 

 ends. Spores formed as in T. clavata, AcJilya, etc., but discharged 

 by the breaking away of a considerable part of the end of the spor- 

 angium, caused by the swelling of an apical group of spores, after 

 wdiich the spores maj' emerge immediately or may come to rest to 

 emerge several days later. Usually a few seconds after the cracking 

 of the sporangium the spores of the tip ooze out in a group exactly 

 as in Thraustofheca. The spores next below this apical group now 

 swell, extending somewhat the truncated tip of the sporangium and 

 after a few seconds begin to move out in their turn. This continues 

 in a series of partial discharges involving a few layers of spores each 

 time until in about five to ten minutes all the spores become loosened 

 and most of them discharged from the sporangium tip where they are 

 spread out in a loose irregular colony. A few spores are always left 

 in the sporangia. The spores encyst in irregular, not spherical, forms 

 before emerging, and are not connected by threads as in Achlya, but 

 exhibit a distinct mutual attraction while emerging as shown for 

 Dictyuchus by Weston (Ann. Bot. 32: 155. 1918). They slide over 

 each other and shift their relative positions but always keep in con- 

 tact with the emerging mass. Spores usually emerging from their 

 cysts immediately upon discharge, some of them coming out of their 

 cysts even while being pushed from the sporangium. The emergence 

 from the cysts is much more rapid than in Achlya or Saprolegnia, 

 occupying only about ten seconds. Gemmae not observed. Oogonia 

 formed rarely under laboratory conditions, spherical or slightly ob- 



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