CHAP. XL TRANSMITTED EFFECTS ; CUCUKBITA. 537 



24 '3 mm.., whilst the mean increase of those with greased tips 

 was 20*7 mm. The grease, therefore, slightly checked the 

 growth of the terminal part, but this part was not much 

 injured; for several radicles which had been greased for a 

 length of 2 mm. continued to grow r during seven days, and were 

 then only a little shorter than the controls. The appearance 

 presented by these radicles after the seven days was very 

 curious, for the black grease had been drawn out into the finest 

 longitudinal striae, with dots and reticulations, which covered 

 their surfaces for a length of from 26 to 44 mm., or of 1 to 

 1*7 inch. We may therefore conclude that grease on the tips 

 of the radicles of this Phaseolus somewhat delays and lessens 

 the geotropic curvature of the part which ought to bend 

 most. 



Gossypium herbaceum. The raiicles of this plant bend, 

 through the action of geotropism, for a length of about 6 mm. 

 Five radicles, placed horizontally in damp air, had their tips 

 touched with caustic, and the discoloration extended for a 

 length of from f to 1 mm. They showed, after 7 h. 45 m. and 

 again after 23 h., not a trace of geotropism ; yet the terminal 

 portion, 9 mm. in length, had increased on an average to 

 15 '9 mm. Six control radicles, after 7 h. 45 m., were all plainly 

 geotropic, two of them being vertically dependent, and after 

 23 h. all were vertical, or nearly so. 



Cucurbita ovifera. A large number of trials proved almost 

 useless, from the three following causes: Firstly, the tips of 

 radicles which have grown somewhat old are only feebly geo- 

 tropic if kept in damp air ; nor did we succeed well in our 

 experiments, until the germinating seeds were placed in peat 

 and kept at a rather high temperature. Secondly, the hypocotyls 

 of the seeds which were pinned to the lids of the jars gradually 

 became arched ; and, as the cotyledons were fixed, the movement 

 of the hypocotyl affected the position of the radicle, and caused 

 confusion. Thirdly, the point of the radicle is so fine that it is 

 difficult not to cauterise it either too much or too little. But 

 we managed generally to overcome this latter difficulty, as the 

 following experiments show, which are given to prove that a 

 touch with caustic on one side of the tip does not prevent the 

 upper part of the radicle from bending. Ten radicles were laid 

 horizontally beneath and on damp friable peat, and their tips 

 were touched with caustic on the upper side. After 8 h. all 

 were plainly geotropic, three of them rectangularly; after 19 h. 



