PROTOZOA OF LATEX PLANTS 265 



YEAST BROTH 



Bread yeast (Fleischmann's compressed yeast) . 5.0 gms. 



Water 95.0 gms. 



Sodium chloride 0.5 gm. 



Glucose i.o gm. 



Sterilize twenty minutes at fifteen pounds pressure in a steam autoclave. 

 The sugar may be omitted but is desirable because it promotes vigorous 

 growth. 



Cultures maintained in this readily prepared medium are of 

 interest because the organisms are not given blood as a constituent 

 of their food supply, and because the medium may be sterilized by 

 heat. 



Maintenance in plant hosts. A specialized technique is involved 

 in the maintenance of latex flagellates in their plant hosts under 

 laboratory and greenhouse conditions. Herpetomonas elmassiani 

 (Migone) occurs in the field in Asclepias syriaca as far north as 

 New Jersey on the Atlantic Coast. Since this plant is unsuited 

 for greenhouse use on account of winter dormancy, a better host 

 plant for experimental work is Asclepias curassavica, a species 

 used in this country as an annual ornamental, seeds of which 

 can be obtained readily from seedsmen. In the greenhouse this 

 plant Hves many years. Plants grown from seed are fortunately 

 free from flagellates even when the seed is derived from infected 

 plants. This is explained by histological examinations which show 

 that there is never a connection between the old latex cells of the 

 parent plant and the tissues of the seed. The seedlings are easily 

 infected by allowing infected insects of the genus Oncopeltiis to 

 feed on them. About two weeks after an infective feeding flagel- 

 lates begin to be conspicuous in the latex, though they may be 

 found in small numbers at the end of one week. The plants will 

 remain infected indefinitely if given proper care. When the growth 

 becomes too tall each large plant may be used as a source of 

 several smaller ones by making cuttings and rooting these. The 

 stem is cut with a sharp knife into sticks about six inches in 

 length; a few leaves are allowed to remain near the top of each 

 cutting. The pieces of stem are placed in sand so that they are 

 two-thirds covered, the leaves being near the surface of the root- 

 ing medium. The sand is moistened regularly to avoid uneven 

 soaking or drying until new roots form. In four weeks most 

 of the cuttings form roots. Then the new plants are transferred to 



