116 W. ZOrF ZUR KENNTNISS DER PHYCOMYCETEN. 



subsequent cultivations made in large vessels at the ordinary room- 

 temperature, hardly a single non-infected specimen could be found 

 after some time, proving that even the above high percentage 

 might be exceeded. This is explained by the immense fertility of 

 the fungus in zoospore production. The disease runs an absolutely 

 fatal course. As regards other species of Bacillaria being affected 

 by the parasite, I was enabled to confirm the fact so far that in 

 each culture a species of straight Synedra, also the curved S. 

 lunularis, a Gomphonema y and a large Pinmdaria were attacked. 

 Nevertheless, the fungus appeared to prefer the Synedra?, particu- 

 larly the larger forms with rich contents, as well as large Pinmi- 

 larice. At any rate, it was only found in a few of the relatively 

 small Gomphonemas. 



The development was uninterruptedly followed out, as far at 

 least as the formation of swarm-spores. 



It appears to be a special characteristic of these Olpidiea? that, 

 under favourable conditions of nutrition, their vegetative portion 

 forms a sac which attains a relatively considerable length. I have 

 frequently observed individuals whose mycelial sacs extended to 

 nearly the entire length of the largest forms of the Synedrce under 

 consideration, that is to say, 200 /x or more. Such like sacs, in the 

 form of thick vermiform threads, so strikingly resemble the mycelial 

 stages of many Ancylistea? (particularly Pfitzer's A. Closterii, as 

 well as many forms of Lagenidinm Rabenhorstii), that at first, 

 before knowing their development, I was inclined to regard them 

 as the receptacles of these fungi. They are always unbranched, 

 probably for the reason that their relative thickness, as compared 

 with the lumen of the host-cell, allows of too little space for the 

 development of lateral axes. Under unfavourable conditions of 

 nutrition, mostly due to more than one parasite occupying the same 

 foster plant, the mycelial sacs are much curtailed in length, 

 occasionally becoming reduced indeed to quite short, spindle- 

 ellipsoidal, or even spherical bodies often of extreme minuteness. 

 The latter mostly occurs when the parasites invade a Synedra 

 whose contents have already been more or less consumed by one or 

 several larger individuals, or when they develop in great numbers 

 in the host-cell. 



For instance, in the rich material at my disposal I often met 

 with Synedrce in which 20 to 30 were present, yet which at first 

 only occupied a part of the foster-cell. That these truly dwarf- 



