BOTANY OF THE CEYLON PATANAS. 433 
With a view to verifying these deductions, the subaerial parts 
of eighty species, all Dicotyledons except two, have now been 
submitted to anatomical examination. Of these, thirty-three 
were found only on the “dry” patanas, twenty-eight only on 
those above 4500 ft., that is to say “wet” patanas, while 
nineteen are common to both. The number of plants thus 
examined represent about two-fifths of the Dicotyledons of the 
whole patana flora. 
The ordinary anatomical peculiarities of leaves subjected to 
strong insolation are by this time quite familiar to biologists. 
As Heinricher* and others have shown, sun-leaves frequently 
tend to assume an erect position and have a correspondingly iso- 
bilateral structure. The Table which follows shows, in a striking 
manner, a similar relation between the structure and position 
of erect and semi-erect leaves of certain of the patana plants— 
a point to which further reference will be made. A marked 
character of leaves exposed to strong sunlight is the great 
development of palisade-tissue usually at the expense of the 
looser spongy elements. Hence the relative thicknesses of 
these two constituents of the mesophyll is of interest. The 
leaf, as a whole, is thicker in sun- than in shade-plants. 
The development of intercellular spaces is usually greater 
in shade- than in sun-leaves. The epidermal cells, also their 
outer walls and cuticles, attain their greatest thickness in 
sun-leaves. The lateral walls of the epidermal cells are, as a 
rule, straight in sun-leaves and more or less wavy in shade- 
leaves. In dorsiventral sun-leaves the stomata are almost, if 
not entirely, confined to the lower surface. 
Special attention has been paid to these characters, and the 
results are arranged in the form of a table, which includes exact 
measurements of the thickness of the epidermal, palisade, and 
spongy layers of the leaves. So far as we are aware, no 
representative portion of the flora of any biologically uniform 
area has previously been submitted to a systematic examination 
of this character; it is on this account the more desirable to 
place these measurements on record. Interesting comparisons 
will be possible when similar data for other areas are available. 
* Heinricher, Pringsh. Jahrb. Bot. xv. (1884). 
