. Journal of Agricultural Research. X i, 100. C.—Monembrjonically developing egg in 3 2-cell blastula stage with two paranuclearmasses in the trophamnion. Host tissue omitted. X 1,100. D.—Blastula stage of embryo. Note the breaking up of the paranucleus into smallermasses. X550. E.—Embryo at the time of formation of germ layers. X550. F.—En toto drawing of U-shaped embryo within its trophamnion. One large par-anuclear mass is located above it. X108. G.—Outline drawing of a parasite larva with paranucleus. The trophamnion hasbecome reduced to a thin membrane. X60. 54486—23 2 PLATE 5Platygasier
. Journal of Agricultural Research. X i, 100. C.—Monembrjonically developing egg in 3 2-cell blastula stage with two paranuclearmasses in the trophamnion. Host tissue omitted. X 1,100. D.—Blastula stage of embryo. Note the breaking up of the paranucleus into smallermasses. X550. E.—Embryo at the time of formation of germ layers. X550. F.—En toto drawing of U-shaped embryo within its trophamnion. One large par-anuclear mass is located above it. X108. G.—Outline drawing of a parasite larva with paranucleus. The trophamnion hasbecome reduced to a thin membrane. X60. 54486—23 2 PLATE 5Platygasier hiemalis A.—Photomicrograph of twin embryos which have developed side by side betweenfat bodies of the host. The embrj^os are typically U-shaped and slightly advanced indevelopment of the one shown at F on Plate 4. X 140. B.—Photomicrograph of a through three embryos in one end of a host the thickened trophamnion of the embryo on the left. X 116. Twinning and Monembryony in Platygaster liiemalis. Plate 5 ^ Journal of Agricuitural Researcti Washington, D . C. PATHOGENICITY OF OPHIOBOLUS CARICETI IN ITSRELATIONSHIP TO WEAKENED PLANTS By H. R. RosRN and J. A. Elliott, Arkansas Agricultural Experiment Station In the United States the Australian take-all of wheat was firstreported in 1920 ^ (6)/ from New York. The following year it was dis-covered by the writers in Arkansas.^ As the field observations stronglysuggested that the fungus, Ophiobolus cariceti, found on diseased wheat,was a weak parasite, attacking plants which were more or less unthrifty,experiments were undertaken to obtain more information on this point. When Ophiobolus was first found in this country it was regarded withsuch alarm that gasoline was poured over the infested area and theplants burnt (6). This measure doubtless was justified inasmuch as thedisease had been considered a serious one by investigators in Australiaand in European countries, and the discoverers may have had
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