94 Studies in Variegation. I, 



Part I. Reversal in Periclinal Chimaeras. 



Variegated plants having a white subepidermal layer extending 

 over a green core, however fertilised, give exclusively white or albino 

 offspring, which of course die after a short existence. Conversely those 

 having a green skin over a white core give green offspring only. The 

 significance of this observation was first emphasized by Baur. We have 

 seen numerous examples of such behaviour in the course of our work, 

 of which a list will eventually be given. 



The general appearance of these chimaeras, as Winkler and Baur 

 have called them, is familiar. It is noticeable that in some of them the 

 thickness of the " skin," whether white or green, may remain with great 

 constancy the same over very large areas of leaf-surfaces. In white- 

 skinned forms which are thus regular (e.g. Holly and Box) the deficiency 

 of chlorophyll affects chiefly the subepidermal layer. In other plants 

 (e.g. Nicotiana colossea var. variegata) there is continual irregularity, 

 some leaves having only the subepidermal layer white, while in others 

 the underlying layers are similarly affected to varying depths, in most 

 white-skinned plants the edges of the leaves are solid white throughout 

 their whole thickness, so that each leaf has the white marginal band 

 characteristic of '' varietates albo-viarginatae" as they are styled in 

 horticulture. The width of these white edges is sometimes fairly 

 constant, but generally varies considerably. 



The condition in which the core is white and the skin green is far 

 less common, and hitherto we have seen none in which the green layer 

 is uniformly one cell thick. Generally the edges are for a considerable 

 breadth solid green, the thickness of the green layer diminishing 

 towards the centre of the leaves where the white core shows through, 

 being sometimes entirely exposed (as in Coprosma). Irregular bands 

 of solid green are often prolonged from the margin into the middle of 

 such leaves. Several of the green-skinned chimaeras have the peculiarity 

 that their stems are destitute of chlorophyll or nearly so. For example, 

 in the green-skinned form of Coprosma, of Vinca major, and of one of 

 the Pelargoniums the stems are almost white. In the green-skinned 

 ivy-leaved Pelargonium also chlorophyll is almost entirely absent from 

 the stem, but, owing to a great development of red anthocyanin in the 

 cortex, the stems are a full pink, whereas in the white-skinned form of 

 the same plant the anthocyanin is confined to a thin layer of the cortex 

 in the stem. In connexion with this type of variegation mention 

 should be made of another, somewhat analogous, in which the absence 



