INTRODUCTION 5 



this genus are not perfectly quiescent during and immediately after 

 emeri^ence. A slight amoeboid motion is obser\-able at all times from 

 their initial formation to the appearance of the encysting membrane. 

 Added to this is a certain feeble jerking and rotation due to the presence 

 of cilia that has been recorded by several ol)servers since Cornu first 

 described it in 1872. On page 11 of his monograph Cornu says that 

 these cilia have just enough agility to cause the escape of the spores 

 from the sporangium, thus implying, in error, that they are the cause 

 of the escape. The presence of cilia on the emerging spores of Achlya is 

 strongly asserted by Hartog ('87) who also predicts that they will be 

 found in all species of Achlya and Aphanomyces ('88). 



Hartog also says in the first of these papers that the spores of AcJilya 

 after forming a ball revoke on their long axes for a short time before 

 the cyst is formed, and that sometimes a few spores will detach them- 

 selves and swim away a short distance. In the second paper he says: 

 "When the sporange is discharged near the margin of the hanging drop 

 or in a thin layer of water on a slide, we constantly see single spores escape 

 from the mass, swim away, and encyst apart." This important obser- 

 vation has been frequently o\-erlooked by subsequent workers, but I 

 can confirm it positively for Achlya caroliniana. In this case if the spor- 

 angium is put on the slide in a very thin layer of water the spores will 

 swim slowly apart on emerging and scatter themselves over a limited 

 area near the mouth of the sporangium. By addition of iodine solution 

 the cilia were clearly seen. In the case of Achlya deBaryana I ha\e ('11) 

 recorded the occasional breaking up of the spore mass into scattered groups 

 and the same habit I have often observed in A. racemosa, A. colorata, 

 and -4. hypogyna. and in the last the spores are ciliated on emerging. 

 Humphrey in his monograph also demonstrated the presence of cilia on 

 the escaping spores of Achlya americana, and says, "In ^4. polyandra one 

 can hardly fail to notice the very marked ciliary motion within the sporan- 

 gium during the escape of the spores." It will be noted, however, that in 

 none of these cases do any of the spores swim away regularly and under 

 ordinary circumstances when first discharged. 



In case of bacterial contamination, or foulness from any cause, or 

 where the parts are put in liciuid nutrient media, there is a strong tendency 

 for the spores to be retained in the sporangium, or if discharged for them 

 to sprout at once without a second swimming stage. There has arisen 

 a loose way of speaking of all sporangia when the spores are retained, or 

 even in part retained, as dictiosporangia,a term that should be used 

 only when spores emerge singly through the wall of the sporangium and 

 escape for (what is homologous with) the second swimming stage. As 

 one might expect, there is variation in Dictyiichus itself in this respect, 



