R. P. Gregory 319 



may be hoped that such investigations will lead to opportunitfes for 

 observing the distribution of plastids to the daughter cells, during the 

 division of cells containing mixtures of plastids of different kinds. In- 

 vestigations should also be made into the development and structure of 

 the egg-cells formed in the green, variegated and yellow parts of the 

 plant, and into the process of fertilization. 



In the hypothesis which has been put forward above, the suggestion 

 has been made that the character, which is inherited through the egg- 

 cell only, is inherent in the plastid itself and is therefore handed on to 

 the products of its division ; in other words, that the plastids are self- 

 determining in respect of the character under consideration. But if 

 this is so in regard to characters of a particular class, there are other 

 characters in which it is not the case. The chlorina character of 

 Mirabilis, and the plastid-colours of many flowers, are inherited through 

 both sexes equally and undergo normal segregation. Their inheritance 

 may be expressed in terms of Mendelian factors, and it may be presumed 

 that the means by which they are transmitted is the same as that of 

 other Mendelian characters, whatever that may be. The hypothesis of 

 Correns would assign to the nucleus the function of transmitting the 

 factor, which distinguishes the normal green from the chlorina races of 

 Mirabilis; at the expense, however, of making the assumption that the 

 nucleus alone passes over from the male cell to the egg-cell in fertiliza- 

 tion. The modification of the hypothesis indicated above would suggest 

 that this assumption is unnecessary, in order to explain the jjurely 

 maternal transmission of certain chai'acters of the chlorojjlast, such as 

 those with which we are dealing. On the other hand, it leaves un- 

 touched the question as to the relative parts played by nucleus and 

 cytoplasm in the transmission of ordinary Mendelian characters, among 

 which certain other characters of the plastids are included. 



Part of the expenses of the experiments described in this paper was 

 defrayed by means of grants from the Royal Society and from the 

 British Association. A large number of plants were grown for me at 

 the John Innes Horticultural Institution and I desire to express my 

 great gratitude to the authorities for the facilities which they have 

 continued to extend to me. 



•Journ. of Gen. iv 21 



