266 RESEARCH IN PROTOZOOLOGY 



soil in pots ; when they are established a microscopical examina- 

 tion will show them to be well infected in most instances. If the 

 infection in the original plant was light in the sense that few of 

 the existing latex cells had been infected by insects, some of the 

 cuttings will send out shoots from axillary buds of the stem from 

 which latex flagellates may be entirely absent. This results from 

 the failure of the old infected latex systems to penetrate the new 

 tissues. Such cuttings must be discarded, and in the later growth 

 of each plant branches which show no flagellates in their leaves 

 should be trimmed away. If care is taken to confirm the presence 

 of the flagellates from time to time l3y microscopical examina- 

 tions and to remove branches from which they are absent it is 

 possible to maintain infections in these laboratory plants for years. 

 Asclcpias nivea and hybrids between Asclcpias curassamca and 

 nivca may be used for the same purpose and handled in the 

 same way with success. 



Maintenance in insect hosts. As has been suggested above, it 

 is necessary to maintain colonies of the insect hosts of the flagel- 

 lates in order to secure infection of seedlings when desired. This 

 is done easily for Oncopeltus fasciatus, and probably for other 

 species in the same genus, by means of the following technique : 



During late summer the insects are collected in the field. They 

 may be confined in Erlenmeyer flasks or other laboratory glass 

 containers, for crowding in small jars does not seem to be harmful 

 if food is supplied properly. Dry Asclcpias seeds serve as food; 

 such seeds are easily collected in the fall from native species. 

 When fed on the foliage of plants in the greenhouse many in- 

 sects die, but they thrive on seeds. Fresh drinking water must be 

 provided in abundance. This is best furnished in inverted tubes, 

 each with a small opening at the lower end ; for this purpose 

 test tubes may be melted into the shape shown in Fig. 17 C 

 and hung from the side of the container by a wire or cord. 



Insects collected in the field may or may not be infected with 

 flagellates. To secure an uninfected stock a small amount of cotton 

 is placed in the bottom of the colony jar, where yellow Qgg masses 

 are soon hidden by the fertile females. Before the eggs become 

 orange in color they are removed from the presence of adults 

 to fresh colony jars. Nymphs hatching from these eggs are free 

 of flagellates, ensuring a stock of uninfected insects which can 

 be maintained on seeds and water indefinitely. 



