CHAP. I. 



TROP^EOLUM. 



27 



Fig. 16. 



vertically and coming into close contact. This upward move- 

 ment differs from one of the great diurnal oscillations above 

 described only by the position being permanent during the night 

 and by its periodicity, as it always commences late in the 

 evening. 



Tropxolum minus (?) (var. Tom Thumb) (Tropseoleae). The 

 cotyledons are hypogean, or never rise above the ground. By 

 removing the soil a buried epicotyl 

 or plumule was found, with its 

 summit arched abruptly down- 

 wards, like the arched hypocotyl 

 of the cabbage previously described. 

 A glass filament with a bead at 

 its end was affixed to the basal half 

 or leg, just above the hypogean 

 cotyledons, which were again almost 

 surrounded by loose earth. The 

 tracing (Fig. 16) shows the course 

 of the bead during 11 h. After the 

 last dot given in the figure, the 

 bead moved to a great distance, 

 and finally off the glass, in the 

 direction indicated by the broken 

 line. This great movement, due to 

 increased growth along the con- 

 cave surface of the arch, was caused 

 by the basal leg bending back- 

 wards from the upper part, that is 

 in a direction opposite to the depen- 

 dent tip, in the same manner as 

 occurred with the hypocotyl of 

 the cabbage. Another buried and 



arched epicotyl was observed in the same manner, excepting 

 that the two legs of the arch were tied together with fine silk 

 for the sake of preventing the great movement just mentioned. 

 It moved, however, in the evening in the same direction as 

 before, but the line followed was not so straight. During the 

 morning the tied arch moved in an irregularly circular, strongly 

 zigzag course, and to a greater distance than in the previous 

 case, as was shown in a tracing, magnified 18 times. The move- 

 ments of a young plant bearing a few leaves and of a mature 

 plant, will hereafter be described. 



Tropceolum minus (?) : circum- 

 nutation of buried and arched 

 epicotyl, traced on a horizon- 

 tal glass, from 9.20 A.M. to 

 8.15 P.M. Movement of bead 

 of filament magnified 27 

 times. 



