152 
Notes . 
BOTANICAL NOTES, No. 5.— THE INFLUENCE OF EX- 
TERNAL CONDITIONS ON THE FORM OF LEAVES. — 
When at Singapore, I requested Mr. Ridley to show me some 
examples of plants growing in the Botanic Gardens in a habitat not 
usual to them. In response, Mr. Ridley was good enough to point 
out an undescribed species of Renanthera , to which he proposes to 
give the name of R. albescens , an epiphytic orchid which naturally 
scrambles over plants growing on hot open sandy heaths. The 
specimen had been transferred to the Botanic Garden, where it was 
growing under the shade of a well-foliaged tree. The interest in the 
specimen lies in the fact that on one and the same plant it was possible 
to see the effect of environment on the form of the shoot. The part 
of the shoot which had developed when on the sandy heath consisted of 
a stiff stem bearing short thick leaves separated by short internodes, 
whilst the part of the shoot developed in the garden had longer and 
thinner leaves, which were separated by longer internodes. A table 
will best represent the comparative structure of the two sets of leaves. 
Leaf formed on Sandy Heath. 
60 mm. 
28 mm. 
1-75 mm. 
Leaf formed in the Gardens. 
Length. 120 mm. 
Maximum width. 25*5 mm. 
Thickness. -925 mm. 
Structure. 
} Upper epidermis, with no ( Cuticle half as thick, cells 
stomata. 1 shallower. 
1 layer of flattened cells. 
1 layer of ‘ polygonal ’ 
cells. 
12 layers of large paren- 
chyma-cells, elongated 
at right angles to the 
surface. 
2 layers of small poly- 
gonal cells. 
Mesophyll, of about the / 
same number of layers 
of cells in both leaves ; 
no distinct pallisade- 
cells or spongy paren- j 
chyma ; intercellular \ 
spaces small; scattered 
prosenchymatous cells, 
with thick cellulose- 
walls. 
Several layers of flattened 
cells, merging into large 
polygonal cells, not 
markedly elongated at 
right angles to the sur- 
face. 
2 layers of small poly- 
gonal cells. 
Thick cuticle. 
Many stomata level with 
the surface. 
/ Cuticle half as thick. 
Many stomata slightly 
Lower epidermis. j raised above the sur- 
' face. 
Thus the decrease in thickness of the leaves grown in the gardens 
is occasioned by a change in the form of the cells, and not by 
a diminution in their number. The combined effect of strong sunlight 
