328 



MODIFIED CIKCUMNUTATION. CHAP. VII. 



Fi S- 13 - 



some very young plants 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 buphurifolia. This species 

 is rendered remarkable by the petioles 

 being foliaceous, like the phyllodes 

 of many Acacias. The leaflets are 

 bmall, 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 



Oxalis bupleurifolia : circum- during the remainder of the night 



StfiifiST o P b 8 : - d <-* b <" the move- 



liquely across end of petiole; ment was not sufficient to be called 



movements traced on ver- sleep. The ascending and descend- 



tical glass from 9. A.M. June ing lines did not coinci(ie so that an 



Join to o.oU A.M. zotn. ,,. _ -ill mi 



Apex of leaflet 4* inches elll P se was formed each day. There 



from the glass, so movement was but little zigzagging ; if the 



not much magnified. Plant filament had been fixed longitudi- 



f 



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 

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



