R P. Gregory 309 



a variegated plant, in which the central parts of the leaves were green. 

 In one very young leaf, besides the central patch of green, there was a 

 faint green stripe along the margin of the leaf, and in this region it was 

 found that the epidermal cells alone contained definitely coloured 

 plastids (PL X, fig. 9), those of the deeper layers being nearly colourless, 

 as they usually are in the very young stages of the yellow tissues. 



In most of the variegated plants there occur patches which are 

 intermediate in colour between the full gi-een and the clear yellow 

 (PL IX, figs. 1 — 3). Gradations of this kind are due to the presence of 

 more or fewer layers of normal green cells in particular regions. In one 

 variegated plant the mosaic consisted entirely of patches of full green 

 and lighter green ; that is to say, green cells were present in some 

 layers, at least, in all parts of the plant. 



In the variegated plants, the stems, sepals and other organs, the 

 cells of which contain chloroplasts, have a structure similar to that of 

 the leaves. 



In the pure yellow-leaved plants (i.e. plants which have no normal 

 green plastids at all), the very young stems and leaves are always of a 

 pale yellowish-white colour. The rate of growth of these plants is very 

 slow as compared with that of the variegated plants, and still more so 

 as compared with that of the pure green plants (see PL IX, fig. 3, in which 

 three sister plants of the same age ai-e shewn). Most of the yellow- 

 leaved plants die at an early stage ; in such as survive, the pigmentation 

 of the plastids increases somewhat in the older leaves, which become 

 yellowish-gTeen. Apart fi'om this change with age, various yellow- 

 leaved plants may also shew some slight gi-adation, from a less to a 

 more pronounced greenish tint, which is no doubt due to different 

 degi-ees of chlorosis of the constituent cells. In some ca.ses, plants, 

 which have no normal green cells, have, side by side, cells of different 

 degrees of chlorosis (PL X, fig. 8) ; thus the plant is built up of a patch- 

 work of different kinds of cells, and in that respect is comparable witii 

 a variegated plant, although it is, nevertheless, chlorotic throughout. 



So far as the fully gi'own organs of the variegated plants are con- 

 cerned, no exception has been found to the rule that any particular cell 

 contains chloroplasts of one kind only, though there may be minor 

 variations in the size of the individual chloroplasts. But in the very 

 young, actively growing leaves, evidence has been obtained of the 

 existence, side by side in the same cell, of chloroplasts of different 

 kinds, which differ from one another in the same way as do the chloro- 

 plasts of the normal and of the yellow cells in the mature organs. 



