STUDIES ON THE GENETICS OF FLOWER-COLOURS, ETC. 121 



iiblc to pixxlnce colour iu n small segment of a petal, or iu certaiu few 

 filaiueuts. 



The peculiar conditiou iu pseiulo-wliite seems, as far as my observation 

 goes, to Ije due to a special factor ; the discussion on the latter ^\-ill ]>e 

 resen-ed for a future pai"»er. 



Mutations, etc. 

 As the i-eadei« must luive often noticed in the coiu'se of my description of 

 tlie various crossing experiments we find not imfi'equently a numljer of unex- 

 l^ected indi^•iduals among the oflspring of certaiu crosses : thus, for instance, 

 few magenta or orange plants ai'e 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 Poiiulaca are veiy fine we 

 miglit then have the chance admixtiu-es from coloured plants, though not very 

 probable iu view of the utmost care taken for avoiding such. As the experi- 

 ment-s progi-essal on the cases where imexpacted indi^-iduals are detected have 

 inci-eased to such an extent that we came fiuiilly to the conclusion that they 

 ai-e clearly no chance iulmixtm-es, but normal pro:lucts. Though seed-pans 

 were placet] near each other they were never watered from alcove, and so we 

 must have avoided the danger of hurling down seed? of one pan to the 

 neighbom-ing by tliis process. Nor would it be very probable that seeds were 

 blown do^vn from one pan to another hy wind, since the earth in pans was 

 held constantly moist by keeping them in a vessel partly full of water. If 

 Some coloxired individuals detected among the progeny from white pai'ents 

 were really derived from pans containing seeds taken on colom-ed parents (by 

 wind, etc.) no such fact will certainly occm-, were pans containing seeds of 

 both kinds kept distantly fr'om 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 coloiu'ed plants on the other were 

 kept in some spots of om- Botanical Garden where Podulaca was never 

 cultivated before (thus avoiding the invasion of seeds of the former cultivation) 

 and which are nearly 30 meti-es dista,nt from each other and separated by 

 foiufold high fences. In spite of all these ti-eatments I have found as iLSual 

 several coloured plants among the prc^ny of white parents. 



