336 FRANCIS O. HOLMES. 



in which the relative positions of nucleus and parabasal body 

 could be definitely determined, the organism was constantly a 

 herpetomonad. Smears of the insect flagellate confirmed this, 

 for in them the position of the organelles could be determined in 

 every single case far more readily than in sections of the gland. 

 This question is not quite safely settled, for at some other season 

 of the year the evidence might differ from that which I have 

 been able to gather, but with the knowledge of the exact part 

 of the insect parasitized, the dorsal and anterior thirds of the 

 thoracic salivary gland, and the extent of infection during the 

 season at which the insects are busily feeding on the infected 

 plants, it will be easier to work on the questions concerned with 

 the insect host of the flagellate. 



SUMMARY. 



Histological studies of the milkweed host of the flagellate 

 Herpetomonas elmassiani (Migone) showed that the organisms 

 were confined to the latex system, in which they were intracellular 

 but not intracytoplasmic. The latex is secreted into the general 

 cell vacuole of the latex duct, and it is in this that the organisms 

 were found. No other cells or parts of cells were found to 

 be penetrated. 



During the early part of the summer one or a very few latex 

 cells in a plant were sometimes infected, for in Asclepias the 

 original latex cells of the embryo never fuse. Because of this 

 condition occasional localized infections appeared, in which a 

 few leaves of the infected plant were found to be free from 

 organisms. 



The flagellates of Oncopeltus fasciatus (Dall.), a red and black 

 hemipterous insect suspected of being the insect host of H. 

 elmassiani (Migone), were found to inhabit the three-lobed 

 thoracic salivary gland. In the gland these were definitely 

 localized, colonizing only the dorsal and anterior lobes. 



REFERENCES CITED. 

 Franga, C. 



'14 La flagellose des euphorbes. Archiv. f. Protistenkunde, 34: 108-132. 

 Holmes, F. O. 



'24 Herpetomonad Flagellates in the Latex of Milkweed in Maryland. Phyto- 

 pathology, 14: 146-151. 



