The Power of Movement in Plants, Charles Darwin [the reading list book TXT] 📗

nearly one inch to the right, and a new tracing was begun (B). From this time, viz., 7 A.M. August 2nd to 8.20 A.M.

on the 4th,

 

* We were led to observe this plant by Dr. Carl Kraus’ paper, ‘Beitr�ge zur Kentniss der Bewegungen Wachsender Laubbl�tter,’ Flora, 1879, p. 66. We regret that we cannot fully understand parts of this paper.

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the leaf manifestly circumnutated. It does not appear from the diagram that the leaves move periodically, for the descending course during the first two nights, was clearly due to epinastic Fig. 113. Pinus pinaster: circumnutation of young leaf, traced from 11.45

A.M. July 31st to 8.20 A.M. Aug. 4th. At 7 A.M. Aug. 2nd the pot was moved an inch to one side, so that the tracing consists of two figures. Apex of leaf 14 � inches from the vertical glass, so movements much magnified.

 

growth, and at the close of our observations the leaf was not nearly so horizontal as it would ultimately become.

 

Pinus austriaca.—Two leaves, 3 inches in length, but not [page 252]

quite fully grown, produced by a lateral shoot, on a young tree 3 feet in height, were observed during 29 h. (July 31st), in the same manner as the leaves of the previous species. Both these leaves certainly circumnutated, making within the above period two, or two and a half, small, irregular ellipses.

 

(26.) Cycas pectinata (Cycadeae, Fam. 224).—A young leaf, 11 � inches in length, of which the leaflets had only recently become uncurled, was observed during 47 h. 30 m. The main petiole was secured to a stick at the base of the two terminal leaflets. To one of the latter, 3 3/4 inches in length, a filament was fixed; the leaflet was much bowed downward, but as the terminal part was upturned, the filament projected almost horizontally.

The leaflet moved (see Fig. 114) largely and periodically, for it fell until about 7 P.M. and rose during the night, falling again next morning after 6.40 A.M. The descending lines are in a marked manner zigzag, and so probably would have been the ascending lines, if they had been traced throughout the night.

 

Fig. 114. Cycas pectinata: circumnutation of one of the terminal leaflets, traced from 8.30 A.M. June 22nd to 8 A.M. June 24th. Apex of leaflet 7 3/4

inches from the vertical glass, so tracing not greatly magnified, and here reduced to one-third of original scale; temp. 19o - 21o C.

 

CIRCUMNUTATION OF LEAVES: MONOCOTYLEDONS.

 

(27.) Canna Warscewiczii (Cannaceae, Fam. 2).—The movements of a young leaf, 8 inches in length and 3 � in breadth, produced by a vigorous young plant, were observed during 45 h. 50 m., as shown in Fig. 115. The pot was slided about an inch to the right on the morning of the 11th, as a single figure would have been too complicated; but the two figures are continuous in time. The movement is periodical, as the leaf descended from the early morning until about 5 P.M., and ascended during the rest of the evening and [page 253]

part of the night. On the evening of the 11th it circumnutated on a small scale for some time about the same spot.

 

Fig. 115. Canna Warscewiczii: circumnutation of leaf, traced (A) from 11.30

A.M. June 10th to 6.40 A.M. 11th; and (B) from 6.40 A.M. 11th to 8.40 A.M.

12th. Apex of leaf 9 inches from the vertical glass.

 

(28.) Iris pseudo-acorus (Irideae, Fam. 10).—The movements of a young leaf, rising 13 inches above the water in which the plant grew, were traced as shown in the figure (Fig. 116), during 27 h. 30 m. It manifestly circumnutated, though only to a small extent. On the second morning, between 6.40 A.M. and 2 P.M. (at which latter hour the figure here given ends), the apex changed its course five times. During the next 8 h. 40 m.

it zigzagged much, and descended as far as the lowest dot in the figure, making in its course two very small ellipses; but if these lines had been added to the diagram it would have been too complex.

 

Fig. 116. Iris pseudo-acorus: circumnutation of leaf, traced from 10.30

A.M. May 28th to 2 P.M. 29th. Tracing continued to 11 P.M., but not here copied. Apex of leaf 12 inches beneath the horizontal glass, so figure considerably magnified. Temp. 15o - 16o C.

(29.) Crinum Capense (Amaryllideae, Fam. 11).—The leaves of this plant are remarkable for their great length and narrowness: one was measured and found to be 53 inches long and only 1.4 broad at the base. Whilst quite young they stand up almost vertically to the height of about a foot; afterwards

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their tips begin to bend over, and subsequently hang vertically down, and thus continue to grow. A rather young leaf was selected, of which the dependent tapering point was as yet only 5 � inches in length, the upright basal part being 20 inches high, though this part would ultimately become shorter by being more bent over. A large bell-glass was placed over the plant, with a black dot on one side; and by bringing the dependent apex of the leaf into a line with this dot, the accompanying figure (Fig. 117) was traced on the other side of the bell, during 2 � days. During the first day (22nd) the tip travelled laterally far to the left, perhaps in consequence of the plant having been

 

Fig. 117. Crinum Capense: circumnutation of dependent tip of young leaf, traced on a bell-glass, from 10.30 P.M. 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 � h. During the next 24 h. it travelled 2 � 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.

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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.

 

(33.) Pontederia (sp.?) (from the highlands of St. Catharina, Fig. 118. Pontederia (sp.?): circumnutation of leaf, traced from 4.50 P.M.

July 2nd to 10.15 A.M. 4th. Apex of leaf 16 � inches from the vertical glass, so tracing greatly magnified. Temp. about 17o C., and therefore rather too low.

 

Brazil) (Pontederiaceae, Fam. 46).—A filament was fixed across the apex of a moderately young leaf, 7 � inches in height, and its movements were traced during 42 � h. (see Fig. 118). On the first evening, when the tracing was begun, and during the night, the leaf descended considerably.

On the next morning it ascended in a strongly marked zigzag line, and descended again in the evening and during the night. The movement, therefore, seems to be periodic, but some doubt is thrown on this conclusion, because another leaf, 8 inches in height, appearing older and standing more highly inclined, behaved differently. During the first 12 h.

it circumnutated over a

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small space, but during the night and the whole following day it ascended in the same general direction; the ascent being effected by repeated up and down well-pronounced oscillations.

 

CRYPTOGAMS.

 

(34.) Nephrodium molle (Filices, Fam. 1).—A filament was fixed near the apex of a young frond of this Fern, 17 inches in height, which was not as yet fully uncurled; and its movements were traced during 24 h. We see in Fig. 119 that it

 

Fig. 119. Nephrodium molle: circumnutation of rachis, traced from 9.15 A.M.

May 28th to 9 A.M. 29th. Figure here given two-thirds of original scale.

 

plainly circumnutated. The movement was not greatly magnified as the frond was placed near to the vertical glass, and would probably have been greater and more rapid had the day been warmer. For the plant was