Damping Off. 321 



TLis peculiarity in the development of the zoospores is one which 

 has not heretofore been recorded except in a preliminary paper by 

 the writer. 15 jj^e species was at that time studied along with the 

 seedling fungus, A. debaryanus (Hesse), and as this is reported as 

 occurring also on fern prothallia {Todea africana) the species now 

 under discussion was then supposed to be the same, and to this 

 Bpecies it was doubtfully refei-red. But the development of the 

 conidia is very different from that described f(;r any other species of 

 this genus resembling that of Phytojj/ithora as stated above. 



It can not therefore at the present time be said with certainty that 

 the zoospore fonnation in Artotrogu» debaryanus is the same as 

 that found for A. intermedius^ though what evidence we already 

 have on the subject might be interpreted to support that view of 

 the case. 



Where the soil is kept very damp and the air of the house is 

 quite humid the prothallia are apt to be overrun by certain algae 

 which choke the prothallia, shut out the air and Kght, prevent their 

 proper development and frequently cause them to be completely 

 sterile. Many of the prothallia are thus killed, sometimes entire 

 beds or pots of them. A very common alga which I have several 

 times observed is a variety of Ilormisoia flaccida (Kuetz.) Lagerh. 

 Species of Oscillatoria are also frecjuently present and produce a 

 like injury. 



If the pots or vessels in which the prothallia are grown are rested 

 on sphagnum, a layer of which can be placed in the bottom of the 

 wardian case, and after the young prothallia have started, all of the 

 watering be applied through this, the prothallia will do much better 

 than if surface watering is practiced and far better than where the 

 pots are rested in a vessel partly full of water. The air of the 

 wardian case or of the house should not be kept too damp. 



KoTE ON THE GeNUS AbTOTROGUS. 



Hesse, who first ^Q?,Q,Y\\ie(i Artotrogus deharyanus'^^ [Pythium de- 

 haryanum Hesse) says, as stated above, that the zoospores are oval 

 and provided with one cilium, PythiuTn equiseti^'^ Sadebeck, 

 which is generally considered to be the same plant, possesses two 



15 Preliminary note on the swarm spores of Pythium and Ceratiomyxa, Bof. 

 Gaz. XIX, 375, 1894. 



Pythiam debaryanum, etc. Halle, 1874. 

 "'■'^ Untersuchungen tiber Pythium equiseti, Cohn's Beitr. z. Biol, d, Pfl. Ill, 117. 



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