Chap. XI. TRANSMITTED EFFECTS : ZEA. 539 



affected by tlie caustic ; the other five were still strictly hori- 

 zontal. After 24 h. 40 m. the three with only slightly discolourrd 

 tips were bent down rectangularly; the other five were not in 

 the least aifectod, but several of them had grown rather tor- 

 tuously, though still in a horizontal plane. The eight cauterised 

 radicles which had at first a mean length of '36 inch, after 9 h. 

 had increased to a mean length of '79 inch; and after 24 h. 

 40 m. to the extraordinary mean length of 2 inches. There 

 was no plain difference in length between the five well cau- 

 terised radicles which remained horizontal, and the three with 

 slightly cauterised tips which had become abruptly bent down. 

 A few of the control radicles were measured after 25 h., and 

 they were on an average only a little longer than the cauterised, 

 viz., 2'19 inches. "We thus see that killing the extreme tip of 

 the radicle of this plant for a length of about 0'5 mm., though it 

 stops the geotropic bending of the upper part, hardly interferes 

 with the growth of the whole radicle. 



In the same box with the 15 control specimens, the rapid geo- 

 tropic bending and growth of which have just been described, 

 there were six radicles, about '6 inch in length, extended hori- 

 zontally, from which the tips had been cut off in a transverse 

 direction for a length of barely 1 mm. These radicles were 

 examined after 9 h. and again after 24 h. 40 m., and they all 

 remained horizontal. They had not become nearly so tortuous 

 as those above described which had been cauterised. The 

 radicles with their tips cut off had grown in the 24 h. 40 m. as 

 much, judging by the eye, as the cauterised specimens. 



Zea mays. — The tips of several radicles, extended horizontally 

 in damp air, were dried with blotting-paper and then touched 

 in the first trial during 2 or 3 seconds with dry caustic ; but 

 this was too long a contact, for the tips were blackened for a 

 length of rather above 1 mm. They showed no signs of geo- 

 tropistn after an interval of 9 h., and were then thrown away. 

 In a second trial the tips of three radicles were touched for a 

 shorter time, and were blackened for a length of from 0"5 to 

 0'75 mm. : they all remained horizontal for 4 h., but after 8 h. 

 30 m. one of them, in which the blackened tip was only 0'5 mm. 

 in length, was inclined at 21° beneath the horizon. Six con- 

 trol radicles all became slightly geotropic in 4 h., and strongly 

 so after 8 h. 30 m., with the chief seat of curvature generally 

 between 6 or 7 mm. from the apex. In the cauterised specimens, 

 the terminal growing part, 10 mm. in length, increased during 



