374 Insects and Potato Foliage 



between them, but only between the individuals composing a particular 

 series. The series comprise : 



Series I. Plants raised from seed obtained from both good and 

 bad plants, Edinburgh. 



Series 11, Plants raised from seed obtained from good plants, 

 Dunbar. 



Series III. Plants raised from seed obtained from bad plants, 

 Dunbar. 



The distribution of Aleurodes is shown below. 



Distribution of Aleurodes. Series I — III. 



No. of plants in series 

 I II III Total 



Total 22 17 23 62 



There is not any very marked difference between the three series 

 and we may look at the whole 62 plants together; 



There are 18 with no Aleurodes in any stage. 

 Nine in which eggs and flies are abundant, scale few, 

 Fourteen in which scale is abundant only, 

 Six in which both scale and eggs are both noticeable. 

 Without unduly straining the figures we may say that the plants 

 have been unequally selected by the flies of each brood and that there 

 is a very high percentage (29) of plants that have been avoided: is 

 this selection correlated with any plant character that can be noted? 

 We have been unable to find any character of the plants which we 

 can correlate with the presence or absence of either the scale form or 

 the eggs : clearly there is a connection between the presence of Aphis 

 and the discoloration of the veins : there is no connection between the 

 blotching and the presence of either Aphis or Aleurodes ; and there is 

 not any character that we could note which is correlated with a marked 

 presence or absence of either the scale form of Aleurodes or its eggs. It 

 has been possible to note only certain physical characters : it is possible 

 that there is a character connected with the condition of the leaf surface, 

 or the texture of the leaf, or the composition of the cell substance or sap 



