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Show 218 CIRCUMNUTATION OF STOLONS. CHAP. IV. on a cloudy dn.y, became distinctly curved towards the light, and were therefore heliotropic. Close in front of the tips of tho prostrate stolons, a crowd of very thin sticks and the dried haulms of grasses were driven into tho sand, to represent the crowded stems of surrounding plants in a state of natmo. This was done for the sake of observing how the growing stolons would pass through them. They did so easily in tho course of 6 days, and their circumnutation apparently facHitated their passage. When the tips encountered sticks so close together that they could not pass between them, they rose up and passecl over them. The sticks and haulms were removed after the passage of tho four stolons, two of which wore found to have assumed a permanently sinuous shape, and two wore still straight. But to this subject we shall recur under Saxifmga. Sax1;fraga sarmentosa (Saxifragero).-A plant in a suspended pot had omitted long branched stolons, which depended like Fig. 88. Saxifrar;a sarmontosa : circum nutation of an incl ined stolon, traced iu darkness on a horizontal glass, from 7.45 A.M. April 18th to 9 A.M. on 19th. Movement of end of stolon magnified 2·2 times. threads on all sides. Two were tied up so as to stand vertically, and their upper ends became gradually bent downwards, but so slowly in the course of several days, that the bending was probably due to their weight and not to geotropism. A glass filnr ment with little triangles of paper was fixed to the end of one of these stolons, which was 1 n inches in length, and had already become much bent down, but still projected at a considm:able angle above the horizon. It moved only slightly three tunes from side to side and then upwards; on the following day CHAP. IV. CIRCUMNUTATION OF STOLONS. 219 the movement was even less. As this stolon was so long wo thought that its growth was nearly completed, so we triecl another which was thicker and shorter, viz., lOt inches in length. It moved greatly, chiefly upwards, and chang d its course five times in the course of the day. During the night it curved RO much upwards in opposition to gravity, that the movement could no longer be traced on tho vertical glass, and a horizontal one had to be used. The movement was followed cluring the next 25 h., as shown in Fig. 88. Throe irregular olUpscs, with their longer axes somewhat differently directed, were almost completed in the first 15 h. Tho extreme actual amount of movement of tho tip dming the 25 h. was ·75 inch. Several stolons were laid on a flat surface of damp . ·and, 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 e~countering a stone or other obstacle on tho ground, short ~1eces of smoked glass, an inch in height, were stuck upright mto the sand in front of two thin lateral branches. Their tips scratched the smoked surface in various directions; ono made three upward and two downward lines, besides a nearly horizo~ tal one; the other curled quite away from tho 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 mo:ed to ~he right, and after ascending, descended vertically; ultunately It passed round one end of the glass instead of over it. th Many long pins were next driven rather close together into e 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 passa{)'e · aton e P1a ce I· t was forced to tlll'n at right angles to its formo er' course; at another place it could not pass throuo·h the pins and th e hm' d er part became bowed; it then omvoe d upwards' a~d pas~ed through an opening between tho upper part of some pms WhiCh happened to diverge; it then descended and finally :enme ;1ge~ through the crowd. This stolon was rendered pormaY smuous to a slight degree, and was thicker whore sinuous be an elsewhere, apparently from its longitudinal growth havino· en checked. 0 Cotyledon umbilicus (Crassulacere).-A plant growing in a pan |
