PROTOZOA OF LATEX PLANTS 269 



the slides may be stained as though they held sections of tissues, 

 using iron hematoxylin, Delafield's hematoxylin, Giemsa's stain, 

 or other standard stains. 



PROBLEMS FOR INVESTIGATION 



Effect of latex protozoa on the health of the host plants. Per- 

 haps the most important question which presents itself is that of 

 the effect of latex protozoa on the health of the host plant. Lafont, 

 the original discoverer of latex flagellates in Euphorbia pihdifera, 

 believed that the infected plants were noticeably harmed by the 

 presence of the organisms. In this view some later workers con- 

 curred; these were Franga (1911), who worked with E. segetalis, 

 and Gaschen (1926), who studied E. cyparissias and E. gerardiana. 

 It will be noticed that these investigators worked with flagellates 

 in plants of the genus Euphorbia. No report of injury to one of 

 the ASCLEPiADACE^ has been published. A considerable number 

 of workers reported that the infected euphorbias with which they 

 worked showed no macroscopic symptoms distinguishing them 

 from uninfected plants of the same species ; among these investiga- 

 tors were Leger (1911) who worked with E. pilulifera, Bouet and 

 Roubaud (1911) with the same plant, Franga (1911) with E. 

 segetalis, Rodhain and Bequaert (1911) with E. indica, Noc and 

 Stevenel (1911) with E. pilulifera, and Aubertot (1927) with 

 E. cyparissias. 



To avoid errors in such work a number of precautions must be 

 taken. Injury due to transplanting or cultivating under unfavorable 

 conditions must be avoided. Many of the hosts of latex flagellates 

 are weeds not commonly cultivated. Such wild plants do not always 

 respond favorably to the treatment given to garden species. A 

 sufficient number of uninfected plants must therefore be main- 

 tained as controls to show that the experimenter has been success- 

 ful in handling the host plant itself and in protecting it from in- 

 juries due to abnormal environmental conditions other than the 

 flagellate infection. Excessive insect injury due to the feeding of 

 the insect host of the flagellates must be differentiated from pos- 

 sible injury caused by the protozoa themselves. Thus in infecting 

 species of Asclcpias by means of Oncopeltiis fasciatus infected 

 with Herpetomonas elmassiani an excessive number of insects on 

 a young plant or on the tender growing shoot of an older plant 

 sometimes causes wilting and even death of the top of the plant. 



