328 



MODIFIED CIKCUMNUTATION. 



Chap. VII 



some Tery young plauts the rise did not commence until late 

 at night. We have seen that the cotyledons, instead of sink- 

 ing like the leaflets, rise up vertically at night. 



Oxalis bupleurifolia, — This species 

 fig. 130. is rendered remarkable by the petioles 



^•^ being foliaceous, like the phyllcdes 



of many Acacias. The leaflets are 

 t.mall, of a paler green and more 

 tender consistence than the folia- 

 ceous 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 

 has actually occurred with those of 

 another Brazilian species, 0. rusci- 

 formis. Nevertheless, in the present 

 species the nyctitropic movements 

 are perfectly performed. The folia- 

 ceous 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 the night, and fell 

 during the remainder of the night 

 and early morning; but the move- 

 ment was not sufficient to be 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 longitudi- 

 nally, we should probably have seen 

 th^t there was more lateral move- 

 ment than appears in the diagram. 

 A. terminal leaflet on another leaf was next observed (the 

 •wtiole being secured), and its movements are shown in 

 Pig. 131. During the day the leaflets are extended horizon- 

 tally, and at night depend vertically ; and as the petiole rises 

 during the day the leaflets have to bend down in the evening 



/ 



Oaaiis bupleurifolia: circum- 

 nutation of foliaceous pe- 

 tiole, filament fixed ob- 

 liquely across end of petiole; 

 movements traced on ver- 

 tical glass from 9. A.M. June 

 26th to 8.50 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^°- 

 24^" C. 



