CHAP. X 



APOGEOTROPISM. 



499 



Fig. 185. 



horizontally, and the upper part of the stem rose 58 in 46 h., 

 in the manner shown in the accom- 

 panying diagram (Fig. 185). "We here 

 see that during the whole of the 

 second day of 152 h., the stem plainly 

 circumnutated whilst bending upwards 

 through apogeotropism. It had still 

 to rise considerably, for when the last 

 dot in the figure was made, it stood 

 32 from an upright position. 



Plialaris Canariensis. A cotyledon 

 of this plant (1*3 inch in height) has 

 already been described as rising in 

 4 h. 30 m. from 40 beneath the hori- 

 zon into a vertical position, passing 

 through an angle of 130 in a nearly 

 straight line, and then abruptly be- 

 ginning to circumnutate. Another 

 somewhat old cotyledon of the same 

 height (but from which a true leaf 

 had not yet protruded), was similarly 

 placed at 40 beneath the horizon. For 

 the first 4 h. it rose in a nearly straight 

 course (Fig. 186), so that by 1.10 P.M. 

 it was highly inclined, and now apo- 

 geotropism acted on it with much less 

 power than before, and it began to 

 zigzag. At 4.15 P.M. (i.e. in 7 h. from 

 the commencement) it stood vertically, 

 and afterwards continued to circum- 

 nutate in the usual manner about the 

 same spot. Here then we have a 

 graduated change from a straight up- 

 ward apogeotropic course into circum- Lilmm auratum : apogeo- 

 nutation, instead of an abrupt change, tropic movement of stem, 

 as in the former case. 



Avena saliva. The sheath-like coty- 

 ledons, whilst young, are strongly apo- 

 geotropic ; and some which were placed 

 at 45 beneath the horizon rose 90 in 

 7 or 8 h. in lines almost absolutely 

 straight. An oldish cotyledon, from which the first leaf began to 



traced on a vertical glass 

 during 2 days and 2 

 nights, from 10.40 A.M. 

 March 18th to 8 A.M. 

 20th. Figure reduced to 

 one-half of the original 

 scale. 



