OCR Text |
Show MODIFIED CIRCUMNUTATION. CIIAP. VII. Rome very young plants the rise did not commence until late at night. We have seen that the cotyledons, instead of sinking like the leaflets, rise up vertically at night. I I I I I I I I I t / // Oxali<J bupleurifolia: circumnutation of foliaceous petiole, filament fixed obliquely across end of petiole; movements traced on vertical glass from 9. A.M. June 26th to 8.1)0 A.M. 28th. Apex of leaflet 4~ inches ti·om the glass, so movement not much magnified. Plant 9 inches high, illuminated from above. Temp. 23!0 - 24j0 c. Oxalis bupleurifolia.-This species is rendered remarkable by the petioles being foliaceous, like the phyllodes of many Acacias. The leaflets are 8mall, of a paler green and more tender consistence than the foliaceous petioles. The leaflet which was observed was ·55 inch in length, and was borne by a petiole 2 inches long and · 3 inches broad. It may be suspected that the leaflets are on the road to abortion or obliteration, as bas actually occurred with those of another Brazilian species, 0. rusci· formis. Nevertheless, in tho present species the nyctitropic movements are perfectly performed. The foliaceous petiole was :first observed during 48 h., and found to be in continued circumnutation, as shown in the accompanying figure (Fig. 130). It rose during the day and early part of tho night, and fell during tho remainder of the night and early morning; but the movement was not sufficient to bo called sleep. The ascending and descend· ing lines did not coincide, so that an ellipse was formed each day. There was but little zigzagging; if the filament ·had been fixed lo~gitudi· nally, wo should probably have seen that there was more lateral move· ment than appears in the diagram. A terminal leaflet on another loaf was next observed (t~e petiole being secured), and its movements are show~ m Fig. 131. During the day the leaflets are extended honz?n· tally and at night depend vertically; aud as the petiole rJ~es dur~g the day the leaflets have to bend down in the evemng CHAP. VII. SLEEP OF LEA YE '. 329 more than 90°, so as to assume at night their vertical position. On the first day the leaflet simply moved up and down; on tho Fig. 131. I I I I / I I / I 1/ I / I / / ./ l -;:B ·= ..c: E~ ~ · C'I - Q) '-t:l c ::l ~~ := t:l ~ 0 !; ;;i 2 .q <.>c:. ·ta ..t; ? ·- t.= ~~ ~ ~ "'=''biJ t:l co=~ ·-=c .!~: (.) c;: ~ g ~ ~ § ~ ;: "'=' g '(j ~ ~ .. ~~ ~- ~ ti~ .~ ·;: ~ §-t::<l> ' ..0 "' 5 I I ~~ ~ I I ~ 1 I O seconddayit pl . 1 . after whi amY mrcumnutated between 8 A.l'ri. and 4.30 P.M., ch hour the great evening fall commenced. |