Four stolons still attached to the plant were laid on damp sand in the back of a room, with their tips facing the north-east windows.  They were thus placed because De Vries says* that they are apheliotropic when exposed to the light of the sun; but we could not perceive any effect from the above feeble degree of illumination.  We may add that on another occasion, late in the summer, some stolons, placed upright before a south-west window

* ‘Arbeiten Bot Inst., Würzburg,’ 1872, p. 434. [page 218]

on a cloudy day, became distinctly curved towards the light, and were therefore heliotropic.  Close in front of the tips of the prostrate stolons, a crowd of very thin sticks and the dried haulms of grasses were driven into the sand, to represent the crowded stems of surrounding plants in a state of nature.  This was done for the sake of observing how the growing stolons would pass through them.  They did so easily in the course of 6 days, and their circumnutation apparently facilitated their passage.  When the tips encountered sticks so close together that they could not pass between them, they rose up and passed over them.  The sticks and haulms were removed after the passage of the four stolons, two of which were found to have assumed a permanently sinuous shape, and two were still straight.  But to this subject we shall recur under Saxifraga.

Saxifraga sarmentosa (Saxifrageae).—­A plant in a suspended pot had emitted long branched stolons, which depended like

Fig. 88.  Saxifraga sarmentosa:  circumnutation of an inclined stolon, traced in 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 filament with little triangles of paper was fixed to the end of one of these stolons, which was 17 ½ inches in length, and had already become much bent down, but still projected at a considerable angle above the horizon.  It moved only slightly three times from side to side and then upwards; on the following day [page 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., 10 1/4 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