CHAP. IV. CIRCUMNUTATION OF STOLONS. 219 



the movement was even less. As this stolon was so long we 

 thought that its growth was nearly completed, so we tried 

 another which was thicker and shorter, viz., 10i inches in length. 

 It moved greatly, chiefly upwards, and changed its course five 

 times in the course of the day. During the night it curved so 

 much upwards in opposition to gravity, that the movement 

 could no longer be traced on the vertical glass, and a horizontal 

 one had to be used. The movement was followed during the 

 next 25 h., as shown in Fig. 88. Three irregular ellipses, with 

 their longer axes somewhat differently directed, were almost 

 completed in the first 15 h. The extreme actual amount of 

 movement of the tip during the 25 h. was *75 inch. 



Several stolons were laid on a flat surface of damp sand, in the 

 same manner as with those of the strawberry. The friction of 

 the sand did not interfere with their circumnutation ; nor could 

 we detect any evidence of their being sensitive to contact. In 

 order to see how in a state of nature they would act, when 

 encountering a stone or other obstacle on the ground, short 

 pieces of smoked glass, an inch in height, were stuck upright 

 into the sand in front of two thin lateral branches. Their tips 

 scratched the smoked surface in various directions ; one made 

 three upward and two downward lines, besides a nearly hori- 

 zontal one; the other curled quite away from the glass; but 

 ultimately both surmounted the glass and pursued their original 

 course. The apex of a third thick stolon swept up the glass in a 

 curved line, recoiled and again came into contact with it ; it then 

 moved to the right, and after ascending, descended vertically ; 

 ultimately it passed round one end of the glass instead of over it. 



Many long pins were next driven rather close together into 

 the sand, so as to form a crowd in front of the same two thin 

 lateral branches; but these easily wound their way through 

 the crowd. A thick stolon was much delayed in its passage ; 

 at one place it was forced to turn at right angles to its former 

 course; at another place it could not pass through the pins, 

 and the hinder part became bowed ; it then curved upwards 

 and passed through an opening between the upper part of some 

 pins which happened to diverge ; it then descended and finally 

 emerged through the crowd. This stolon was rendered perma- 

 nently sinuous to a slight degree, and was thicker where sinuous 

 than elsewhere, apparently from its longitudinal growth having 

 been checked. 



Cotyledon umbilicus (Crassulaceje). A plant growing in a pan 



