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. 



