STUDIES ON THE GENETICS OP FLOWER-COLOURS, ETC. 
121 
able to produce colour in a small segment of a petal, or in certain few 
filaments. 
The peculiar condition in pseudo-white seems, as far as my observation 
goes, to be due to a special factor ; the discussion on the latter will be 
reserved for a future paper. 
Mutations, etc. 
As the readers must have often noticed in the course of my description of 
the various crossing experiments we find not unfrequently a number of unex¬ 
pected individuals among the offspring of certain crosses : thus, for instance, 
few magenta or orange plants are often seen among the progeny derived from 
seeds taken on selfed flowers of white parents, etc. At the beginning of my 
experiments it was thought that since seeds of Portulaca are very fine we 
might then have the chance admixtures from coloured plants, though not very 
probable in view of the utmost care taken for avoiding such. As the experi¬ 
ments progressed on the cases where unexpected individuals are detected have 
increased to such an extent that we came finally to the conclusion that they 
are clearly no chance admixtures, but normal products. Though seed-pans 
were placed near each other they were never watered from above, and so we 
must have avoided the danger of hurling down seeds of one pan to the 
neighbouring by this process. Nor would it be very probable that seeds were 
blown down from one pan to another by wind, since the earth in pans was 
held constantly moist by keeping them in a vessel partly full of water. If 
Some coloured individuals detected among the progeny from white parents 
were really derived from pans containing seeds taken on coloured parents (by 
wind, etc.) no such fact will certainly occur, were pans containing seeds of 
both kinds kept distantly from each other. The following experiment made 
in 1920 may be of some interest : pans which contain seeds of whites on the 
one hand and those which contain seeds of coloured plants on the other were 
kept in some spots of our Botanical Garden where Portulaca was never 
cultivated before (thus avoiding the invasion of seeds of the former cultivation) 
and which are nearly 30 metres distant from each other and separated by 
fourfold high fences. In spite of all these treatments I have found as usual 
several coloured plants among the progeny of white parents. 
