iO 



CIECUMNUTATION OF SEEDLINGS. 



Chap. L 



Fig. 29. 



pressed alternately witlt greater and less force on them. There 

 must, therefore, have been movement in at least two planes at 

 right angles to one another. These radicles were so delicate that 

 they rarely had the power to sweep the glasses quite clean. One 

 of them had developed some lateral or secondary rootlets, which 

 projected a few degrees beneath the horizon ; and it is an im- 

 portant fact that three of them left distinctly serpentine tracks 

 on the smoked surface, showing beyond doubt that they had 

 circumnutated like the main or primary radicle. But the 

 tracks were st) slight that they could not be traced and copied 

 after the smoked surface had been varnished. 



Hypccotyl. — A seed lying on damp sand was firmly fixed by 

 two crossed wires and by its own growing radicle. The cotyle- 

 dons were still enclosed within the seed-coats; and the short 

 hypocotyl, between the summit of 

 the radicle and the cotyledons, 

 was as yet only slightly arched. A 

 filament ('85 of inch in length) 

 was attached at an angle of 35° 

 above the horizon to the side of 

 the arch adjoining the cotyle- 

 dons. This part would ultimately 

 form the upper end of the hypo- 

 cotyl, after it had grown straight 

 and vertical. Had the seed been 

 properly planted, the hypocotyl at 

 this stage of growth would have 

 been deeply buried beneath the 

 surface. The course followed by 

 the bead of the filament is shown 

 in Fig. 28. The chief lines of 

 movement from left to right in the 

 figure were parallel to the plane 

 of the two united cotyledons and 

 of the flattened seed ; ard this 

 movement would aid in dragging 

 them out of the seed-coats, which 

 are held down by a special struc- 

 ture hereafter to be described. Tlie movement at right angles 

 to the above lines was due to the arched hypocotyl becoming 

 more arched as it increased in height. The foregoing observa- 

 tions apply to the leg of the arch next to the cotyledons, but 



Cucurbda ovifera : circumnuta- 

 tion of straight and verti- 

 cal iiypocotyl, with 61ament 

 fastened transversely across 

 its upper end, traced in dark- 

 ness on a horizontal glass, 

 from 8.30 A.M. to 8.30 P.M. 

 The movement of the terminal 

 bead originally magnified 

 about 18 times, here only 4^ 

 ^4mes. 



