328 



MODIFIED CIECUMNUTATION. 



Chap. Vli 



/ 



Rome very young plauts the rise did not commence until lata 

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

 ing like the leaflets, rise up vertically at night, 



Oxalis hv/pleurifolia. — This species 

 is rendered remarkable by the petioles 

 being foliaceous, like the phyllodes 

 of many Acacias. The leaflets are 

 miall, 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. rusd- 

 furmis. 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 

 that there was more lateral move- 

 ment than appears in the diagram. 

 A terminal leaflet on another leaf was next observed (the 

 petiole being secured), and its movements are shown in 

 Fig. 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 



0."ali* linjjU'urifot'ii : circum- 

 nutation of foliaceous pe- 

 tiole, iilanieut fixed ol>- 

 iiqiiely across end of petiole; 

 movements traced on ver- 

 tical glas? from 9. A.M. .June 

 26th to 8..50 A.M. 28th. 

 Apex of leaflet 4^ inches 

 from the glass, so movement 

 not much magniiiod. Plant 

 9 inches high, illuminated 

 from above. Temp. 23J°- 

 24i° C. 



