98 Studies in Variegation. I. 



have, for instance, several hundred yards of Euonymus radicans, var. 

 variegata used as an edging-plant. Wholly green shoots are common 

 on this plant, and wholly white shoots not rare, but no reversal has yet 

 been seen. Among many hedges of white-skinned holly also no reversal 

 was found. 



Cases superficially mistakable for reversals are not uncommon in 

 various plants. For example, in the white-skinned Pelargonium used 

 by Baur in his observations (of which he kindly gave me a cutting some 

 years ago) leaves like that shown in Fig. 15 occasionally appear. At 

 first sight the condition recalls that of Figs. 11 and 16, but on closer 

 examination this is seen to be due in reality to the formation of small 

 solid green areas associated with irregularity in the number of layers 

 devoid of chlorophyll. In this variety, as in many white-skinned forms 

 the appearance of wholly green areas is not very rare. 



Obviously the occurrence of reversal, and of areas wholly green or 

 wholly white, are consequences of some instability arising in the growing 

 point, but there is nothing to indicate the cause of such instabilities. 

 The formation of wholly green areas in white-skinned plants may no 

 doubt be described as a bursting out of the green core, and might be 

 attributed to some greater vigour of the green parts, but these expres- 

 sions are merely descriptive. Injury may be suggested as a probable 

 cause. White shoots do indeed arise with special frequency round old 

 scars on the boles of white-skinned hollies, but green shoots, which might 

 be expected to burst through are extremely rare, if they occur at all in 

 such places. The suggestion of injury is plainly inapplicable to such 

 cases as the Pelargoniums described in this paper. 



It would be interesting to ascertain whether the green-skinned forms 

 ever change back again, and the absence of any example of this trans- 

 formation may be worth noting. 



As mentioned in introducing the subject, the consequence of somatic 

 reversal is that the genetic properties of the plant are completely 

 changed. Naturally this fact leads to a surmise similar to that sug- 

 gested by the behaviour of root-cuttings \ In the variegated chimaeras 

 we can visually distinguish the properties of the cortex, but is it not 

 probable that similar genetic distinctions may exist which are not thus 

 visible ? May not the phenomenon of reversal exist in regard to them 

 also, bringing into the cortex, and so into the germ-cycle, properties 

 previously contained only in the deeper layers ? 



1 See "Root-Cuttings, Chimaeras, and Sports," Jour. Gen. Vol. vi. 1916, p. 75. 



