88 THE SAPROLEGXIACEAE 



differs in the smaller oogonia and smaller, centric eggs, as well as in other 

 less conspicuous characters. It will be noted that this species as well 

 as /. unispora differs from Achlya not only in the motility of the primary 

 spores, but also in the frequent extension of threads through empty 

 sporangia, although this does not lead to the formation of nested sporangia. 



4. Isoachlya monilifera (deBary) Kauffman. Am. Journ. Bot. 8: 231. 

 1921. 

 Saprolegnia monilifera deB. Bot. Zeit. 46:629, pi. 9, fig. 6. 1888. 



Pl axes 25 AND 50 



Vegetative growth short; main hyphae I3-22(jl in diameter near base. 

 .Sporangia scarce, often entirely absent, short or moderately long, usually 

 largest near the tip; in older cultures the sporangia often proliferating later- 

 ally below as in Achlya. Spores i i-i i .8iJ. in diameter. Oogonia abundantly 

 produced in a very dense zone immediately surrounding the substratum, 

 appearing before the sporangia, mostly in chains, the lower elements 

 of the chain usually smaller and sometimes remaining as gemmae, com- 

 monly spherical with or without a basal neck, rarely elongated inside 

 old sporangia (in collection No. i of January 15, 1913, on corn meal 

 agar, some of the oogonia were irregular in outline) ; diameter about 

 40-93(i,, most about 50-6511., a large part of them breaking off more or 

 less completely from the hyphae and from each other after the maturity 

 of the eggs; walls yellowish-brown when old, smooth, slightly or not 

 at all pitted. Eggs 1-12 in an oogonium, mostly 2-6, 17.7-33.5iA in 

 diameter, average about 23-2511., extremes sometimes occurring in the 

 same oogonium, yellowish-brown, centric, with two rows of small drop- 

 lets all the way around or subcentric, with one row on one side and two on 

 the other. Gemmae abundant in all cultures, spherical, pear- or club- 

 shaped, very often borne in chains; upon change of condition they may 

 become sporangia, discharging their spores through a lateral papilla. 

 Antheridia not developed. 



Easily distinguished from all others by the yellowish-brown 

 oogonia borne in chains which separate wholly or in part from each 

 other at an early stage, and by the absence of antheridia. DeBary's 

 figure does not show the structure of the eggs. The species has not been 

 recognized heretofore in America. 



Not rare in ponds, meadows, and small streams, such as pond across 

 road in front of cemetery, branch back of athletic field, and Glen Burnie 

 meadow. Collected in Chapel Hill 26 times between February 29, 1912, 

 and December 16, 1913 (see table, p. 14). Found several times since. 



This is undoubtedly the true S. monilifera, and agrees in all essen- 

 tials with deBary's description. In one of our collections (marsh at foot 

 of Lone Pine hill, February 17, 1921) a good many of the oogonia with 

 young eggs were parasitized by the penetration of a slender, non-septate 

 fungus which destroyed the eggs and completely filled the oogonia with 



