R P. GrRECxORY 321 



Fig. 10. Section of a very young variegated leaf, examined in the fresli state. The 

 section represents a group of cells at the junction between a patch of green tissue and 

 the surrounding chlorotic tissue. The cells A and B contained (1) bright green 

 chloroplasts of the normal type, with well-developed starch-grains, and also (2) smaller 

 plastids, c, c, c, of a pale colour and with little starch, which were indistinguishable 

 from the pale-coloured plastids of the cell C. In most of the plastids of the cell C 

 the pigment was readily recognizable, but in a few, d, d, d, no colour could be detected 

 with certainty. The plastids of the cell D were, for the most part, nearly colourless 

 in appearance, but three or four, c, «, c, could pass for the pale-coloured kind found 

 in C. The cells C and D, therefore, contained plastids differing from one another in 

 the degree of chlorosis. E and F were also chlorotic cells, as were all the cells on 

 this side of the section. The plastids of E were of the pale-coloured type ; in none of 

 those of F could any colour be detected with certainty, x 650. 



Figs. 11 — 18 are drawn from very young variegated leaves, examined in fixed and 

 stained preparations. The material was cut in hard paraffin, so as to avoid, as far as 

 possible, the risk of crushing the cells and consequently displacing the chloroplasts from 

 the cells to which they properly belonged. No indication was obtained that any dis- 

 placement had taken place, and all cells, the walls of which were ruptured, were rejected. 

 The sections were cut so as to pass through adjacent patches of normal and chlorotic 

 tissue. The stains employed were Carbolic Fuchsin and Light Green. This method did 

 not give any definite differential coloration as between the normal and chlorotic plastids, 

 BO that it was necessary to rely upon differences in size as the distinguishing feature. The 

 figures represent cells containing chloroplasts of different sizes ; all these cells were found 

 at the junction between the normal and the chlorotic tissues. In certain cases, where two 

 smaller chloroplasts lie close together in a pair, it was not always possible, with the method 

 of staining employed, to say whether they were chlorotic plastids, or whether they were 

 the products of a recent division of a normal plastid ; but it is clear that the possibility 

 of accounting for some of the small plastids in this way only applies in the minority 

 of cases. This sort of difficulty is much less in preparations of fresh material, where the 

 differences in colour form an additional guide. Figs. 11 — 18 are all x 650. 

 Fig. 11. The chloroplast, x, is a large one seen in end view. Near it is another large 

 one and also a small one, both seen in face view. The two smaller chloroplasts to 

 the left of the cell may be the products of the recent division of a normal one. 

 Fig. 12. Cell containing two large chloroplasts and several small ones. The two chloro- 

 plasts at (/) were in different planes, near the upper and the lower walls of the cell 

 respectively. 

 Fig. 13. The palisade cells (above) contain only small chloroplasts. Below, to the right, 

 are three cells containing large chloroplasts, some of which are seen sideways or 

 end-on. To the left are two cells each containing both large and small chloroplasts. 

 Fig. 14. Cell containing several large and one small chloroplast. All the chloroplasts 



contained in this cell are shewn in the figure. 

 Fig. 15. The four chloroplasts shewn were in focus together. 

 Fig. 16. Cell containing four large and five small chloroplasts. 

 Fig. 17. Cell with three large chloroplasts and several small ones. 



Fig. 18. The cell shewn in the middle had chloroplasts of different sizes ; those above had 

 chlorotic plastids, those below large ones only. 



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