May 22nd to 10.15 A.M. 25th. Figure not greatly magnified.
disturbed; and the last dot made at 10.30 P.M. on this day is alone here given. As we see in the figure, there can be no doubt that the apex of this leaf circumnutated.
A glass filament with little triangles of paper was at the same time fixed obliquely across the tip of a still younger leaf, which stood vertically up and was as yet straight. Its movements were traced from 3 P.M. May 22nd to 10.15 A.M. 25th. The leaf was growing rapidly, so that the apex ascended greatly during this period; as it zigzagged much it was clearly circumnutating, and it apparently tended to form one ellipse each day. The lines traced during the night were much more vertical than those traced during the day; and this indicates that the tracing would have exhibited a nocturnal rise and a diurnal fall, if the leaf had not grown so quickly. The movement of this same leaf after an interval of six days (May 31st), by which time the tip had curved outwards into a horizontal position, [page 255] and had thus made the first step towards becoming dependent, was traced orthogonically by the aid of a cube of wood (in the manner before explained); and it was thus ascertained that the actual distance travelled by the apex, and due to circumnutation, was 3 1/8 inches in the course of 20 ½ h. During the next 24 h. it travelled 2 ½ inches. The circumnutating movement, therefore, of this young leaf was strongly marked.
(30.) Pancratium littorale (Amaryllideae).--The movements, much magnified, of a leaf, 9 inches in length and inclined at about 45o above the horizon, were traced during two days. On the first day it changed its course completely, upwards and downwards and laterally, 9 times in 12 h.; and the figure traced apparently represented five ellipses. On the second day it was observed seldomer, and was therefore not seen to change its course so often, viz., only 6 times, but in the same complex manner as before. The movements were small in extent, but there could be no doubt about the circumnutation of the leaf.
(31.) Imatophyllum vel Clivia (sp.?) (Amaryllideae).--A long glass filament was fixed to a leaf, and the angle formed by it with the horizon was measured occasionally during three successive days. It fell each morning until between 3 and 4 P.M., and rose at night. The smallest angle at any time above the horizon was 48o, and the largest 50o; so that it rose only 2o at night; but as this was observed each day, and as similar observations were nightly made on another leaf on a distinct plant, there can be no doubt that the leaves move periodically, though to a very small extent. The position of the apex when it stood highest was .8 of an inch above its lowest point.
(32.) Pistia stratiotes (Aroideae, Fam. 30).--Hofmeister remarks that the leaves of this floating water-plant are more highly inclined at night than by day.* We therefore fastened a fine glass filament to the midrib of a moderately young leaf, and on Sept. 19th measured the angle which it formed with the horizon 14 times between 9 A.M. and 11.50 P.M. The temperature of the hot-house varied during the two days of observation between 18 1/2o and 23 1/2o C. At 9 A.M. the filament stood at 32o above the horizon; at 3.34 P.M. at 10o and at 11.50 P.M. at 55o; these two latter angles being the highest and the lowest observed during the day, showing a difference of 45o. The rising did not become strongly marked until between
* 'Die Lehre von der Pflanzenzelle,' 1867, p. 327. [page 256]
5 and 6 P.M. On the next day the leaf stood at only 10o above the horizon at 8.25 A.M., and it remained at about 15o till past 3 P.M.; at 5.40 P.M. it was 23o, and at 9.30 P.M. 58o; so that the rise was more sudden this evening than on the previous one, and the difference in the angle amounted to 48o. The movement is obviously periodical, and as the leaf stood on the first night at 55o, and on the second night at 58o above the horizon, it appeared very steeply inclined. This case, as we shall see in a future chapter, ought perhaps to have been included under the head of sleeping plants.