ROOT STRUCTURES 69 



are made up of many parallel longitudinal filaments about 45 A 

 thick (PI. XI Vc). The large root arises under peripheral fibrils 9, 1 

 and 2 (i.e. on the side away from the effective stroke of the beat), 

 while the two smaller roots arise under fibrils 5 and 6 and shortly 

 join the large root. At about the level at which the three roots 

 join, the whole root structure bifurcates in the plane of the two 

 central fibrils (i.e. at right angles to the plane of the beat) forming 

 two long roots which run down to about the level of the cell 

 nucleus, where they end freely. This root arrangement has 

 interesting functional implications, for the roots are positioned 

 in such a way that they can best resist the strains caused by the 

 contractions of the shaft fibrils at different parts of the ciliary 

 beat ( see p. 151). 



Some additional unstriated root fibrils are also present in the 

 frontal cells of the gill of Anodonta. These fibrils appear tubular 

 and are about 230 A in diameter, i.e. they are like the unstriated 

 fibrils found in ciliated protozoa, and they also resemble the 

 central fibrils of the cilium in that they appear to consist of a 

 two -strand helix. In some cases at least, they were observed to 

 have connexions with the tips of the basal feet of the cilia (PI. lib), 

 although the basal bodies did not appear to be regularly linked 

 together. Gibbons could not find any similar fibrils in non- 

 ciliated cells of the gill surface. 



In epithelial cells of the mouse oviduct, Toji (1957) found 

 short non-striated rootlets, about 170 A in diameter, which leave 

 the basal body and run in a bundle into the cytoplasm. Similar 

 rootlets found by Rhodin and Dalhamn (1956) attached to the 

 basal bodies of rat tracheal cilia seem to be continuous with the 

 peripheral fibrils in the wall of the basal body. In neither case 

 were the rootlets seen to make contact with any other structure. 



Flagella of Protozoa , Algae and Plant Spermatozoids 



It is especially obvious in the smaller flagellated cells that the 

 roots are serving for anchorage, since they may be attached to any 

 of the more permanent structures in the cell, such as the nucleus, 

 plastids and the cell surface, although this does not preclude other 

 functions for the root fibrils. Thus, in the small unicellular alga 

 Micromonas, a faintly striated fibril runs from the base of the 

 single flagellum to end on the surface of the nucleus, while, in the 



