70 ACTION OF THE EADICLE. CHAP. IL 



growing part continues to do so, probably for as long 

 as growth continues. This movement of the radicle 

 has been described in Brassica, ^Esculus, Phaseolus, 

 Vicia, Cucurbita, Quercus and Zea. The probability 

 of its occurrence was inferred by Sachs,* from radicles 

 placed vertically upwards being acted on by geotro- 

 pism (which we likewise found to be the case), for if 

 they had remained absolutely perpendicular, the attrac- 

 tion of gravity could not have caused them to bend to 

 any one side. Circuinnutation was observed in the above 

 specified cases, either by means of extremely fine fila- 

 ments of glass affixed to the radicles in the manner 

 previously described, or by their being allowed to 

 grow downwards over inclined smoked glass-plates, on 

 which they left their tracks. In the latter cases the 

 serpentine course (see Figs. 19, 21, 27, 41) showed 

 unequivocally that the apex had continually moved 

 from side to side. This lateral movement was small 

 in extent, being in the case of Phaseolus at most 

 about 1 mm. from a medial line to both sides. But 

 there was also movement in a vertical plane at right 

 angles to the inclined glass-plates. This 'was shown 

 by the tracks often being alternately a little broader 

 and narrower, due to the radicles having alternately 

 pressed with greater and less force on the plates. 

 Occasionally little bridges of soot were left across the 

 tracks, showing that the apex had at these spots been 

 lifted up. This latter fact was especially apt to occur 



* 'Ueber das Wachsthum der had previously remarked (* Bti- 



"Wurzeln : Arbeiten des bot. In- trage zur Pflanzenphysiologie,' 



Btituts in Wiirzburg,' Heft iii. 18G8, p. 81) on the fact of radicles 



1873, p. 460. This memoir, be- placed vertically upwards being 



sides its intrinsic and great in- acted on by geotropism, and he 



terest, deserves to be studied as a explained it by the supposition 



model of careful investigation, that their growth was not equal 



and we shall have occasion to on all sides, 

 refer to it repeatedly. Dr. Frank 



