320 Variegation in Primula sineiihiis 



DESCRIPTION OF PLATES. 



PLATE IX. 



Fig. 1. A variegated plant with the green tis.siie nccu|iying the central regions of the 



leaves, the yellow tissue occupying the peripheral part. 

 Fig. 2. A variegated plant shewing a sectorial arrangement of the pure yellow tissue. 

 Fig. 3. Three sister plants from the family 99/12. The plants were of the same age and 



were grown together under the same conditions. They illustrate the difference in the 



i-ate of growth between the pure green (on the left), the variegated (on the right) and 



the pure yellow-leaved (above) plants. 



In the foregoing figures, the arrows point to lines of junction between full green and 

 paler green areas. This difference in colour is due to the presence of more layers of 

 normal green cells in the full green areas than are present in the areas of a lighter green 

 colour. 



PLATE X. 



Figs. 1 — 8 and 10 are from sections of fresh material. Figs. 9 and 11 — 18 are 

 from .stained preparations. All the figures were drawn with the aid of a camera lucida. 



Fig. 1. Chloroplasts from the palisade cells of the leaf of a normal green plant, after 



exposure to bright sunlight, shewing the starch grains. x 650. 

 Fig. 2. Chloroplasts from the palisade cells of a yellow-leaved plant, similarly treated. 



The plastids are much smaller and contain much less starch, x 650. 



Fig. 3. A palisade cell from the leaf of a normal green plant, shewing the chloroplasts 

 after the starch had been removed by keeping the plant dark for some days, x 440. 

 Fig. 4. A cell from the mesophyll of the same plant, x 440. 



Fig. .5. A palisade cell from the leaf of a chlorotic plant for comparison with tig. 3. 

 x440. 



Fig. 6. A cell from the mesophyll of the same chlorotic plant, x 440. 



Fig. 7. Cells from the mesophyll of the leaf of a variegated plant after exposure to sun- 

 light. Two of the cells shewn contain normal green chloroplasts ; the others contain 

 plastids exhibiting various degrees of chlorosis, x 440. 



Fig. 8. Palisade cells from a pure yellow-leaved plant. This yellow-leaved plant con- 

 sisted of a mosaic of cells of different degrees of chlorosis, and in that respect was 

 comparable with a variegated plaut, though it was, nevertheless, quite without normal 

 chloroplasts. Of the three cells shewn, the middle one contained plastids exhibiting 

 an extreme degree of chlorosis; in the plastids of the other two cells the chlorosis 

 was of a less extreme type, x 650. 



Fig. 9. Section through a very young variegated leaf, in a region in which the epidermis 

 alone contained coloured chloroplasts. The well-developed plastids of the epidermal 

 cells are shewn ; all the other cells in this region of the leaf contained only small, 

 chlorotie plastids (see p. 309). x 650. 



