ROOT STRUCTURES 61 



It has been reported that the kinetosomes of some ciUated 

 protozoa may also be able to form trichocysts, which on discharge 

 produce striated fibres with a similar appearance to some root 

 fibres, though the periodicity of the striations is different. Ehret 

 and Powers (1959) found that a transverse section of the tip of a 

 young trichocyst showed an internal fibrillar arrangement similar 

 to that in cilia, and of the same order of size, but with fewer 

 fibrils. 



5. Intracellular Structures Associated with Ciliary Bases 



Almost without exception, the basts of cilia carry some sort of 

 root structure; in some cases these were well known to light 

 microscopists, although only electron microscope studies could 

 show fine structural details. The bases of the flagella of animal 

 sperm are usually closely attached to the nucleus and require no 

 further roots, but the flagella of flagellate protozoa, algae and plant 

 sperm are found to have roots running into the cell cytoplasm. 

 The main function of these roots is undoubtedly one of anchorage ; 

 one has only to observe the vibration of the base of an actively 

 beating cilium to realise that firm anchorage is essential if the 

 cell is to remain intact. Roots usually run towards some permanent 

 and fairly rigid cell structure, or the roots themselves may be 

 very large, e.g. the costa of Trichomonas (see p. 71). Many 

 authors have believed that some of the root structures have a 

 conducting function ; the evidence for this idea will be considered 

 later (see p. 198). 



Protozoan Cilia 



Ciliated protozoa have well developed ciliary roots whose 

 structure and function have been widely studied. All three types 

 of root structure are found here, but in most cases they are limited 

 to the surface layer of the body, probably because of the functions 

 of the cytoplasm, and are modified accordingly. 



A type of very short root structure is found in cirri and mem- 

 branelles, where there are lateral connecting rootlets between the 

 basal bodies of adjacent cilia. In the cirri and membranelles of 

 Euplotes for example (Roth, 1956; 1957), the peripheral fibrils 

 run the full length of the basal body (about 0-33 ju,) and terminate 

 internally at a granule 650 to 900 A in diameter. A second, and 



