452 MESSRS, J. PARKIN AND H. H. W. PEARSON ON THE 
belonging to the erect or semi-erect categories have leaves 
approaching the isobilateral type. 
Lagenophora Billardiert, Gynura Pseudo-china, and, to a less 
extent, Viola Patrinti and Microglossa zeylanica come near iso- 
bilateralism in having both epidermal layers similar, stomata 
numerous on the upper surface, and a feebly differentiated 
mesophyll, which, however, is not compact but loose. In fact, 
except for a fairly thick outer epidermal wall, these plants are of 
a decidedly mesophytic character. From their habitats a meso- 
phytic structure might be expected in the cases of Lagenophora 
and Viola, but hardly in those of Gynura and Microglossa, for 
the one grows on rocks and the other is common on the dry 
patanas. 
The two species of Blumea, Hedyotis verticillaris (P|. 12. fig. 1), 
Polygonum chinense, Senecio ludens, S. zeylanicus, and Vernonia 
Wightiana have leaves with feebly differentiated mesophyll, but 
thickened outer upper epidermal walls ; these all belong to the 
“wet” patanas, and with two exceptions are Composites. 
Flacourtia Ramontchi and Jasminum angustifolium, both of the 
“dry” patanas, have feebly differentiated but compact meso- 
phylls ; leaves inclined to the vertical might have been expected 
in these two species. 
Zornia diphylla has almost an isobilateral structure, both in 
its epidermis and mesophyll, in connection with which it is of 
interest to note that its leaflets move into a profile position 
in. bright sunlight. None of the other plants examined, 
possessing this power of movement, show such a correlated 
structure in their leaflets. Cassia Kleinii and OC. mimosoides 
have their epidermal layers similar, with stomata equally dis- 
tributed on both surfaces, but their mesophyll has a dorsiventral 
differentiation. The four others, Atylosia rugosa (P|. 12. fig. 3), 
Crotalaria rubiginosa, Phaseolus trinervius, and Oxalis corni- 
culata, have practically dorsiventral leaves. It would be 
Interesting to extend these observations to see whether such 
a profile position assumed in bright sunlight may have tended 
to modify the dorsiventrality of such leaves. The above 
examinations merely suggest the idea. 
