VAEIEGATION IN CULTIVATED PLANTS. 329
layers appear to expand and embrace the bundle, but to lose its distinctive blue colour.
Breynia rhamncides a wild species common in Madras, affords another and curious type of variegation. In this the leaves, especially towards the ends of the branchlets are mostly white with dark green patches on the upper side and lighter green ones below. The upper and lower patches do not cover each other and a leaf seen against the light shows sis different shades of green. , The dark green patches of the upper side may be seen even with the naked eye to be definitely raised above general white surface and are due to the presence there of the- paliside tissue which is entirely absent elsewhere. Lighter patches on the lower side are due to the absence of chlorophyll in the spongey parenchyma, which, however, unlike the palisade, is of normal structure throughout. In addition to the two departures from the normal structure there is again, as in the variegated Alocasia a middle layer which, usually green, is white in some patches. Using the same notation as with Alocasia but marking — when a tissue is absent altogether, we find the following variegations to occur : —
G. G. G. G. G. W. G. W. W.
— G. G. — W. G. — W. W.
— G.W.
Conclusion
Variegated leaves of commonly cultivated plants in Madras show that very frequently there are in the leaf not two kinds of mesophyll- tissue as usually stated, but three. And since the chlorophyll may be present or absent independently in these, they appear to be funda- mentally distinct. Though in most plants examined, the middle layer was never found to be white unless one or other of the other two layers are, in Dracaena the middle layer is white in circular patches while the rest is green.
This has the appearance of the green skin over the white core of Enonymus Sp. etc. (Bateson I.e. p. 96), but the sub-epidermal white skin, as distinct from the palisade and spongey tissues as illustrated by Bateson (I.e.) has not been met with.
Explanation of Plate II
Fig. 1. Section through part of the variegated leaf of Maranta vittata, showing normal green tissue on right of a white streak.
Fig. 2. Section* through leaf of Dracaena S2J. Showing absence of chlorophasts in the middle region.
