CHYTRIDIALES 73 



Explanation of Figure 4 



A. Stages in conjugation of isogamous planogametes of Olpidium trifolii 

 Schroeter (zyg., motile bifiagellate zygote). B-F. Rhizophydium ovatum Couch 

 on Stigeoclonium, stages in development of zygote: B, flagellated gamete 

 making contact with young gametangial plant; CD, gametangia enlarged 

 and stained to show nuclei ; E, entrance of gamete of basal gametangium into 

 distal one; F, mature zygote with fusion nucleus and thickened wall. G-I. 

 Rhizophydium couchii, Sparrow on Spirogyra sp., stages in development of 

 zygote : G, two very young gametangia on outer surface of algal wall, with 

 beginnings of rhizoidal systems; H, large receptive gametangium to which is 

 attached small male gametangium; a fertilization tube is clearly visible; 

 /, mature zygote with thickened wall, to which is attached empty male game- 

 tangium. J-O. Rhizophydium granulosporum Scherffel on Tribonema: J, two 

 very young gametangia on outer surface of algal wall, one with rudimentary 

 rhizoidal system; K, immature zygote with adherent male gametangium; 

 L, more mature zygote bearing echinulations on wall; only the male game- 

 tangium appears to have made contact with host; M, similar to preceding 

 but with more peglike spines; TV, immature zygote showing polyandrous con- 

 dition; O, mature thick-walled zygote; both gametangia have here made 

 contact with host wall. P-Q. Zygorhizidium willei Lowenthal on Cylindro- 

 eystis: P, laige female gametangium and small male gametangium on surface 

 of host cell, connected by a conjugation tube produced by the male; Q, 

 mature thick-walled zygote with male gametangium and tube still attached. 

 R-T. Zygochytrium aurantiacum Sorokin: R, early stage in conjugation of 

 lateral branches; gametangia are delimited by cross walls; S, immature zy- 

 gote; T, rough thick-walled mature zygote (zyg.)', two empty sporangia are 

 shown at tips of branches. U, Loborhiza metzneri Hanson on daughter col- 

 onies of Volvox: a, two young gametangia on gelatinous sheath of host 

 colony; b, receptive gametangium forming rhizoidal system, male producing 

 conjugation tube; c, stained receptive thallus showing two gamete nuclei 

 separated by refractive globule; d, binucleate developing resting spore. V-W. 

 Siphonaria variabilis H. E. Petersen in exuviae: V, large, female gametangium 

 receiving contents of smaller male through an anastomosed rhizoid; W, 

 mature thick-walled zygote to which are attached two empty male gametangia. 

 X-Y. Sporophlyctis rostrata Serbinow on Drapamaldia: X, uninucleate game- 

 tangia attached laterally; Y, binucleate spiny-walled zygote. Z-Z '. Polyphagia 

 laevis Bartsch on Euglena (Eu.): Z, male and female thalli attached by con- 

 jugation tube formed by male; Z', later stage of same, showing mature thick- 

 walled zygote which has been formed in distal part of conjugation tube from 

 contents of the two gametangia. 



(A, Kusano, 1929; B-F, Couch, 1935a; G-I, Sparrow, 1933c; J-O, Spar- 

 row, 1939a; P-Q, Lowenthal, 1905; R-T, Sorokin, 1874a, 1883; U, Hanson, 



1944a; V-W, Sparrow, 1943; X-Y, Serbinow, 1907; Z-Z', Sparrow, 1943) 



