CHAPTER XXIX 



PROTOZOA OF LATEX PLANTS 



By 



Francis O. Holmes 

 Boyce Thompson Institute for Plant Research 



INTRODUCTION 



Nature of latex protozoa. The protozoa of latex plants have 

 been studied in many countries since their first discovery. In all 

 cases the organisms have been members of the hemoflagellate genus 

 Herpetomonas. These latex herpetomonads are insect protozoa 

 capable of living in the extensive duct-like vacuoles in the latex 

 cells of milky-juiced plants on which their insect hosts are accus- 

 tomed to feed, just as trypanosomes are typical insect protozoa 

 which spend part of their life-cycle in the blood streams of higher 

 animals. Latex is not like animal blood, however, but is the secre- 

 tion which certain long, branching, multinucleate cells of latex 

 plants pour into vacuoles in their cytoplasm. These vacuoles are 

 continuous, having fused to form an extensive channel within each 

 laticiferous cell except near the growing tips of the plants. The 

 latex does not circulate. Types of latex vary as to dominant con- 

 stituents, but in general there are present resins, fats, wax, 

 caoutchouc, tannin, proteins, alkaloids, mineral salts and sugars in 

 varying amounts. Within the plant the latex is sterile except when 

 the specialized latex herpetomonads have been introduced with the 

 saHvary fluid of plant-feeding insects. 



Latex flagellates live in the latex itself, that is, in the milky 

 contents of the vacuoles of the latex cells. They can neither pene- 

 trate the adjacent cytoplasm, from which they are separated by an 

 extremely thin membrane, nor leave the cell vacuole in which they 

 find themselves to enter the vacuole of an adjacent cell. Once 

 forced from the salivary glands of an insect into the vacuole of a 

 given latex cell of a suitable host plant a latex flagellate has no 



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