316 Variegation in Primula sinensis 



rise by division lo further abnoniial ones, while the products of the 

 division of a normal plastid would be normal. In order to explain the 

 maternal inheritance of this abnormality, it is necessary to adopt 

 the hypothesis, which has met with general acceptance as an cxtcnsiffn 

 of tihe general theoiy of the persistence of plastids, that the plastids of 

 the zygote are derived solely from those present in the unfertilized egg. 

 Thus we should reach an explanaticjn of the fact that thi^ progeny of 

 pure-green normal and pure-yellow chlorotic plants are, respectively, all 

 green and all yellow, no matter what was the character of the male 

 parent. The variegated plants are invariably the offspring ot \aiiegated 

 mothers and they give rise to green, variegated and yellow offspring. 

 The green and the yellow offspring may be explained as originating 

 from egg-cells formed in the pure green or pure yellow patches of tissue 

 which occur in the variegated mother-plant. The variegated offspring 

 must be supposed to have their origin from egg-cells, which are endowed 

 at their formation with a mixture of plastids of different kinds, such as 

 has been found in the cells of the young leaves of the variegated 

 Primulas. The segmentation of a fertilized egg containing different 

 kinds of plastids, each giving rise by its division to plastids of its own 

 kind, would tend to a gradual soi'ting out of the different kinds of 

 plastids into different daughter cells. Eventually, as Baur has pointed 

 out', the great majority of the cells would contain plastids of one or 

 other kind only, and the adult tissues would be a mosaic of cells, the 

 pattern of which would depend upon the distribution in the embryonic 

 cells of the different kinds of plastids. 



The foregoing hypothesis rests primarily upon the general theory of 

 the persistence of plastids from cell to cell in a series of cell-divisions, 

 and the extension of that theory to the effect that the plastids of the 

 adult are genetically derived from those present in the egg. Both the 

 theory and its extension have formed the subjects of an extensive 

 literature with which it is impossible to deal in detail here. Suffice it 

 to say, that the theory of the persistence of the plastids has met with 

 very general support and acceptance for many years. The question has, 

 in some respects, been re-opened by recent investigations on chon- 

 driosomes in plants", but the work which has been done in this direction 

 has not as yet yielded any well-established results ; such as they are, 



1 L.C. p. 349. 



" A general review of this work has recently been given by Cavers, New I'ln/toluyixt, 

 XIII. pp. 96—106 and 170 — 180, 1914. I am greatly indebted to Dr Cavers for his kindness 

 in giving me an advance proof of the second part of his article. 



