310 Variegation in Primula sinensis 



Cells containing different kinds of plastids have been foinul to occur 

 along the lines of junction between gi'oups of green and yellow cells. 

 In such cells, as seen in sections taken from fresh material, the differ- 

 ences are readily recognizable, not only in the size, but also in the 

 colour and starch-content, of the chloroplasts. Fig. 10, PI. X, is from a 

 fresh preparation. In this case, the cells 6', D. E and F contained only 

 chlorotic plastids, but each of the cells A and B contained both large 

 bright-green chloroplasts of the normal type and also smaller pale- 

 coloured plastids (c, c, c), indistinguishable in appearance from the 

 pale-coloured plastids of the chltinitic cells. The chlorotic plastids of 

 the cells C, D, E and F were not all exactly alike, the majority of those 

 contained in the cell C being definitely of a pale yellowish-green colour, 

 while most of those contained in the cell D were nearly or quite colour- 

 less; in each cell, however, both kinds of chloroplast were represented, 

 C containing a few colourless plastids (d, d, d), T) containing a few pale- 

 coloured plastids (c, c, c). The j^lastids of E were jjale-coloured, those 

 of F colourless. The difference between these two kinds of chlorotic 

 plastid is, of course, by no means so sharp as the difference between 

 the chlorotic and the normal plastids; too much stress should not be 

 laid upon it, but it suggests that the plastids of the cells C and D 

 represent a mixture of two kinds of chlorotic plastids, analogous to the 

 mixture of normal and chlorotic plastids found in A and B. 



The use of fresh material for observations ol' the kind just described 

 is open to certain objections, chiefly on account of the risk of confusion 

 due to the displacement of chloroplasts from the cells to which they 

 rightly belong. The observations have, therefore, been checked by the 

 examination of fixed material, cut in parafBn and stained. By the use 

 of this method under suitable precautions the risk of error due to dis- 

 placement of the chloroplasts can be almost eliminated, and systematic 

 searching is much facilitated. The method suffers from the disadvantage 

 that differences of colour between the chloroplasts are no longer recog- 

 nizable and the only distinction is one of size. Even in the very young 

 leaves examined, the enormous majority of the cells contain only one 

 kind of plastid, either large or small, but a certain number of cells have 

 been found, always near the boundary between patches of normal and 

 chlorotic tissue, in which there is no doubt that chloroplasts of different 

 sizes exist side by side. Some of these cells are illustrated in PI. X, 

 figs. 11—18. 



In view of these observations, and their probable significance in 

 relation to the maternal inheritance of variegation, it is desirable that 



