308 Varief/ation in Primula sinensis 



size of the plastids persist after tiie starch has been removed by keeping 

 the plants dark for some days (PI. X, iigs. 3 — 6). 



In the young leaf of the variegated or yi^llow plants the ])lastids of 

 the chlorotic cells are very small and almost colourless (?1. X, figs. !), 13) ; 

 in the older leaves they have increased in size (PI. X, fig. 2) and their 

 pigment is obvious, though they always remain smaller and paler than 

 the typical green plastid. Cells have been found containing plastids 

 which exliibit intermediate degrees of chlorosis (PI. X, figs. 8,10); plastids 

 of this kind are rather larger than in the extreme case and they form 

 lai'ger quantities of starch, though not so nnu-h as do the normal green 

 plastids. 



The variegated and yellow-leaved plants. 



The variegated plants oi Pnviida sinensis shew \ery much the same 

 series of forms as those described by Correns in Mirahilin Jaliipa albo- 

 macidata. The green and yellow cells are mingled in a mosaic, which 

 may be finely divided, small groups of cells of one kind forming tiny 

 flecks scattered among cells of the other kind; or may be coarse, cells 

 of one kind forming patches of considerable size, or even whole leaves 

 or sectors of the plant. When the mosaic is coarse, the component parts 

 may be quite irregularly arranged, but generally there is a tendency 

 towards the formation of a pattern, which, however, is usually not very 

 definite. The rather rare case of a more or less definite sectorial 

 arrangement is illustrated in PI. IX, fig. 2. More coiiiinonly there is a 

 tendency for cells of one kind, either green or yellow, to be distributed 

 about the median line of the leaf the peripheral parts consisting of cells 

 I if the other kind; the boundary between the two parts is nearly always 

 irregulai'. A plant in which the green tissue occupies the middle of the 

 leaf is shewn in PI. IX, fig. 1. In such a plant, yellow cells constitute 

 the whole of the jjeripheral parts of the leaf, and very often the 

 sub-epidermal layer in the green region is also yellow, only the 

 internal layers being green. The plants are not, however, true periclinal 

 chimaeras; the yellow cells are not confined to the peripheral layers, 

 but occur also in other layers and may be scattered sporadically among 

 the green cells, while, conversely, isolated groups of green cells may 

 occur among the yellow cells. As is the case in most plants, the cells 

 of the epidermis (other than the guard cells of the stomata) contain 

 only colourless plastids, even in the normal green leaves ; one curious 

 exception to this rule has, however, been found. The case was that of 



