86 
Keeble . — The Hanging Foliage of 
plane of the leaflet was vertical (downward), {%) the leaflet made 
an angle of about 45 0 with the vertical, (3) the leaflet was 
disposed in a horizontal plane. The following are the results 
of thus enumerating the leaves of four branches of Humboldtia 
laurifolia : 
Leaves Leaves Leaves 
(1) in vertical 
plane. 
Shade branches 8 
Sun branches 2 7 
(2) at 45 0 . 
21 
20 
(3) in horizontal 
plane. 
!9 
o 
there being an average of four pairs of leaflets to each 
pinnate leaf, the total number of leaflets in the various 
positions is: — 
Leaflets Leaflets 
(1) parallel with (2) 45 0 with 
vertical. vertical. 
Shade branches 64 168 
Sun branches 216 160 
Leaflets 
(3) in horizontal Total 
plane. leaves. 
152 =384 
o = 37 6 
or expressed in percentages : 
Leaflets 
(1) (2) 
Shade branches °/ 0 16-6 43.7 
Sun branches °/ 0 57-4 42*5 
( 3 ) 
39.6 = 99.9 
= 99.9 
Hence therefore, what happens in Amherstia nobilis and in 
Brownea grandiceps also occurs in Humboldtia laurifolia , viz. 
the mature position of each leaflet is determined by the 
amount of insolation to which it is exposed : that in all 
these trees this position is arrived at by the amplitude of 
the daily variation of the periodic movement being influenced 
by the amount of light which falls upon the leaves. Intense 
insolation causes great depression of the leaflets, and this 
depression is not fully compensated by the uprising which 
occurs normally during the night. Thus it comes about that 
leaflets exposed, for example, for many days to a bright sun 
assume more and more a position in which the apex points 
downward, and as the inherent power of periodic movement 
wanes the leaflet becomes fixed in this position. If, on the 
other hand, the leaflet is produced in dense shade the periodic 
