— 134 — 



side downwards, thirteen curved upwards (average angle 31"), four 

 curved downwards (average angle 15°) and one did not curve. 



Thus when traumatropism cooperates with geotropism all the 

 specimens curved upwards. When the two tendencies were opposed 

 geotropism was in the majority of cases (13:5) victorious but the 

 curvature was decidedly less than in the first case (31° : 53^). in the 

 four cases in which traumatropism won the curve was smaller than 

 in either of the other classes. 



The existence of traumatic curvatures may have a bearing on 

 my experiments ^) in which continuous curvature of the hypocotyl 

 is produced in Sorghum seedlings supported by their cotyledons. 

 They are usually fixed by being pushed into glass tubes or into 

 grasshaulms, and it is quite likely that injury to the cotyledon may 

 sometimes result. it is impossible that such injury can account for 

 the continuous curvature which is always upwards, but it may be 

 an occasional disturbing cause, especially when the seedlings are 

 in a Position of unstable equilibrium. I pointed out-) that Sorghum 

 supported by their cotyledons in a vertical position, the apex being 

 upwards, should theoreticaily show no curvature, but that such 

 curvature occasionally occurs. We have recently confirmed the 

 Statement made in 1894 (loc. cit.) that when care is taken to keep 

 the cotyledon strictly vertical the average departure from the vertical 

 is small, but an occasional plant shows strong deviation, Thus out 

 of twenty-nine seedlings so treated two deviated from the vertical 

 by 70° and 135" respectively. While the remaining twenty-seven 

 after the same period of 23 hours only departed from the vertical 

 by an average angle of 137". It is possible that the two exceptional 

 cases were due to traumatic action. The same thing may be true 

 for the irregularity observed with plants grown in the dark on a 

 klinostat which are referred to in my paper, loc. cit. p. 572. 



V. Piccard's Melliod. 



We have applied Piccard's ingenious method ■*) to the case of 

 Sorghum with some success. 



In fig. 7, A is the horizontal axis of a Knight's machine 

 carrying the disc D; B is a metal cone, the apex of which is 



'lilg 11H_ UIOV., X>' , J^J 13 a lllClCil L,U11 



^) F. Darwin, Annais of Botany 13, 



-) Ann als of Botany 13, p, 573. 



^) Pringsheims Jahrb. 40, 1904, p. 94. 



p. 567. 



