R P. Gregory 315 



which I have obtained, in the very young leaves of variegated Primulas, 

 of the existence of normal and chlorotic chloroplasts side by side in the 

 same coll, appears to me to afford definite support for the view that the 

 abnormality is localized in the chloroplasts themselves, and is not a 

 function of the cytoplasm as a whole. 



In the present state of our knowledge of the functions of cytoplasm 

 and nucleus, the question is one of some importance. If the maternally 

 inherited character pertains to the cytoplasm in general, as contrasted 

 with the nucleus, the consequence is, as Correns has remarked, strongly 

 to emphasise the importance of the part played by the nucleus, at the 

 expense of any part the cytoplasm might be supposed to play, in the 

 transmission of characters which are inherited through the male and 

 female equally. The hypothesis that this function is limited to the 

 nucleus is, on diverse grounds, regarded favourably by many cytologists, 

 but there are still difficulties to be solved before its complete acceptance 

 can pass unquestioned. Moi-eover, for the present purpose, no assump- 

 tion in this respect need be made, if the view be justified that the 

 abnormality of the chloroplast, which is inherited through the egg-cell 

 only, is localized in the chloroj)last itself. Such a view permits of a 

 modification of Correns' hypothesis, which would serve to account for 

 the' maternal inheritance of the character with which we are dealing, 

 while leaving untouched the question as to the relative functions of 

 nucleus and cytoplasm (apart from the chloroplasts) in the transmission 

 of characters which are inherited in the usual way. 



Since the work of Schimper' and others thirty years ago, the view 

 has gained general support and acceptance that the jDlastids of a plant- 

 cell are persistent cell-organs, in the sense that they are invariably 

 formed by the division of previously existing plastids and are handed 

 down from mother to daughter cell. It is, then, reasonable to suppose 

 that an abnormality inherent in the plastid itself would be handed on 

 to the products of its division^, so that abnormal plastids would give 



' Jahrb.f. wissensch. Bot. xvi. pp. 1 — 247, 1885. Keferences to recent literature con- 

 nected with this subject are given by Cavers, Neic Phytologist, xiii. pp. 96 — 106 and 

 170—180, 1914. 



- If it be granted that the abnormality, with which we are deahng, is inherent in the 

 chloroplast itself, the genetics of the normal, variegated and chlorotic plants provide 

 what amounts to a proof of this proposition. The original variegated plant, which was 

 the offspring of pure green parents, is an exceptional case. But the rarity of such 

 exceptions — only one has occurred among many thousands of plants — and the fact that 

 the partially or completely chlorotic progeny of that plant has continued invariably to 

 throw plants with chlorotic plastids, is additional support for the view that normally the 

 products of the division of a plastid are like the plastid to which they owed their origin. 



