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VARIEGATION IN CERTAIN CULTIVATED PLANTS
M. BALASUBRAMANYAM, B.A., (Hons.), Sacred Heart College, Shembaganur.
The interesting paper by Bateson on Variegation* in certain plants, led me to examine at the instance of Professor Fyson some of the variegate species grown in Madras gardens, for the histological details of the differently coloured patchos.
In Pothos aurea, Linden, the patches of green and yellowish - white parts are not sharply defined, partly because the loss of chlorophyll as one passes from a green to a light part is gradual, and partly because the green occurs in flecks in the light parts, and the light in flecks in the green, so that the leaf has a softly mottled appearance. On the under side the light parts are a little greener than the upper as if the chlorophyll persisted longer on the under side. The palisade on the lighter parts does not lose its characteristic structure but only its colour.
In some other plants the variegation takes the form of white •patches, with very sharply defined edges because the chlorophyll is absent throughout the section. So that the patch is pure white from either side. This occurs for instance in a form of Anthurium Sp. where the white spots are characterised not only by the almost complete absence of chloroplasts, but also by the absence of all differentiation of tissue, the cells being nearly isodiametrie. (PI. II, Fig. 1.)
In Marajita vittata variegation takes the form of narrow white streaks between and parallel to the nerves which run acutely from the mid-rib, only on the upper side. But the palisade tissue loses not only its chlorophyll but also its characteristic form and consists of rounded cells indistinguishable from the spongey parenchyma, except for being colourless. The cells of the water-storage tissue of the upper side are here smaller, and the whole section somewhat thinner. (PI. I, Pig. 1.)
In other species are indications of the existence of a middle tissue, between the upper (palisade) and lower (spongey) tissues of the mesophyll. Thus in a common garden Dracaena, round ill-defined spots of slightly lighter green, about 1/16 in. diameter occur here and there in the leaf. A transverse section shows the normal mesophyll to comprise a layer of obviously elongated cells (the palisade), a second layer of much shorter cells and five or six layers of loosely
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