Page:The Journal of Indian Botany.djvu/376

326 THE JOUKNAL OF INDIAN BOTANY. arranged cells. In the lighter coloured spots a few layers in the middle of the spongey part are without chlorophyll (PI. II, Fig. 2). The effect of the absence of colour in this deep seated portion is to produce lighter spots with hazy, ill-defined outlines.

A variegated form of Alocasia macrorhiza, Schott, said to have arisen as a sport, affords a most interesting variability in the distri- bution of the chlorophyll — deficient tissue. This is always quite definite (as regards each layer of the leaf) without any merging as in Pothos aurea, or haziness as in the Dracaena. Sometimes a plant will give several pure white leaves which, however, soon wither, and are succeeded by more normal ones, or else the plant of course even- tually dies. Sometimes one whole half of a leaf is pure creamy white, without any trace of chlorophyll, while the other half is mottled. More usually the whole leaf is mottled as shown in Plate III. The mottling is in various degrees of lightness, and different on the two sides (compare the upper and under sides of the leaf in the plate).

Sections through different patches show that three regions can be recognised in the mesophyll, an upper (the palisade) a middle and a lower (the spongey-parenchyma). Writing the colours of these three regions in order from the top so that W.G.W. indicates white palisade, green core' and white spongey-parenchma, We find the following combinations to occur : —

G. G. G. G. G. W.

W. G. G. G. W. W.

W. G. W. W. W. W.

W. W. G.

It will be seen that only one of the eight possible combinations is absent, viz., G.W.G., or white core and fully-green cortex.

Though the spongey-parenchyma is thicker than the core, the chlorophyll, is less dense, and in a leaf held up against the light, patches of W.G.W, appear to be nearly of the same tint as those of W.W.G. Again when viewed by reflected light only, patches of G.G.W. appear the same as those of G.W.W., because of the much greater intensity of the green in the palisade tissue than in the middle region, but by transmitted light they are distinguished at once except in the Dracaena referred to above, so far I have not found G.W.G., which would be r ever son, in Bateson's sense of W.G.W.

A variegated Eranthemum Sp. shows the third middle layer even more clearly because the cells are coloured distinctly blue. This causes the leaf to have a dark bluey green colour except round the margin and in patches where the normal green or a lighter colour occurs. Where a vascular bundle traverses the mesophyll the blue