258 RESEARCH IN PROTOZOOLOGY 



alternative to living within this single cell and to multiplying in it 

 indefinitely. Its progeny may invade and colonize the whole length 

 of the cell, including all of its branches, to the growing points 

 where the latex vacuoles are not yet developed. As the cell grows 

 the flagellates may progress with it, invading the new portions 

 as they are formed in the extending tissue, until the progeny of 

 the flagellate originally introduced into a plant may find them- 

 selves many feet away from the site of the insect inoculation. 

 Under laboratory conditions the originally infected portion of an 

 old plant may be cut away and the new growth furnished with 

 roots by regeneration, with the result that the flagellates continue 

 in the new portions of the original cell. The flagellates introduced 

 into latex plants would die with the death of the latex cell and be 

 unable to function in the preservation of the species were it not 

 for the fact that the insect hosts in feeding on the plants occasion- 

 ally suck up latex and flagellates simultaneously, thus completing 

 the cycle. 



Families of plants infected. Latex occurs in the plant families 



EUPHORBIACE^, ASCLEPIADACE^, HORACES, URTICACE^, APOCY- 



NACE.E and COMPOSITE in so many species as to be a well-known 

 characteristic of these plants. In many other families latex is found 

 in occasional species. Latex flagellates have been carefully studied 

 in plants of the euphorbiace^ and of the asclepiadace^, and 

 there have been reports of similar organisms in plants of the genus 

 Ficus in the morace^. Lists of host plants have been given by 

 Lafont (1910), Nieschulz (1925), Gaschen (1926) and Wenyon 

 (1926). 



In the plants of the euphorbiace^ and asclepiadace^ the type 

 of latex system is that known as simple or unfused. In such a 

 system the latex cells never join during their growth, and flagellates 

 present in one cell do not have access to neighboring cells. In other 

 plants, as in the composite, the latex system is of the fused 

 type, in which the latex cells of the entire plant are joined to- 

 gether by frequent fusions of neighboring cells. Latex flagellates 

 have not yet been found in plants with such fused latex cells, 

 but if they should be introduced into any part of such a system 

 they would probably be able to penetrate the whole. It will be of 

 interest to find what phenomena attend infection if such plants 

 are found to contain protozoa in their latex. 



History of discovery. Herpetomonad hemoflagellates were first 



