ACHLVA IT3 



almost always anrlrogynoiis, usually arising from the ooponial stalk it- 

 self, less often from the main hypha; rarely diclinous; antheridia on 

 about 75% of the oogonia, one or two on an oogonium, tuberous; an- 

 theriilial tul>es obvious, penetrating the oogonia and reaching the eggs. 



Tlu' species seems to l)e quite rare, having been recognized only 

 twit-e in considerably over two thousand collections made by us. It was 

 found in some water and trash collected from the west branch above 

 the Meeting of the Waters (No. 6 of Sejitember 26, 1919), and in the 

 same kind of material from the branch in Battle's Park behind Dr. 

 Pratt's residence (Xo. 4 of June 10, 1920). The description has been 

 made from cultures descended from a single spore. 



Our plant can be distinguished (with the unaided eye) from most 

 other Chapel Hill Achlyas by the network appearance gi\-en it by the 

 oogonia. which are e\enly scattered over the entire culture from the 

 bases of the hyphae to the tips. Achlya racemosa approaches this net- 

 work appearance more than any other species of Achlya, Ijut in it the 

 oogonia are not nearly so abundant nor do they extend entirely to the 

 tips of the hyphae. In some species, such as Achlya oblongata or Achlya 

 ecus pic ua, the oogonia are borne in a definite zone near the substratum 

 and from half to two-thirds of the length of the hyphae from the tips 

 backwards are without oogonia. In the Prolifera group the oogonia 

 are scattered more or less over the entire culture, but the big hyphae 

 and long sporangia dissipate the network appearance. 



If we ignore the egg structure, the present species seems to be closest 

 to Achlya polyandra Hildi). The two plants resemble each other in the 

 long, racemose oogonial branches which are recurved at the tip; in the 

 often branched antheridial stalks which arise chiefly from the oogonial 

 branches; and in the smooth oogonial walls which are normally without 

 pits except where the antheridia touch.* The two species are readily 

 distinguished, however, by the difference in the number of eggs in the 

 oogonia, and in the size and structure of the eggs. In Achlya polyandra 

 the number rjf eggs \aries from five to twenty-five, the usual number 

 being ten to fifteen, while in A. Orion the number varies from one to 

 eight, the usual number being one or two. In Achlya polyandra the eggs 

 are said to be centric with an average diameter of 2j[x, but in our plant 

 they are eccentric and most with a diameter of between 33 and 36^1. 

 There are, moreo\er, other differences which are more subject to variation. 

 In Achlya polyandra the sporangia are reported as often not abundant, 

 and secondar>- ones rare; while in our plant both primary and secondary 



*Though pits are rarely seen when the plant is cultivated on flies or grubs they are not 

 at all unusual in cultures on a piece of boiled corn grain. Compare A.flagellata for similar 

 variations. 



