A. 8. HoRNE AND H. M. Lefroy 375 



which does determine whether the fly lays eggs on a plant or not : we 

 believe that there must be some such character which is not revealed by 

 the physical characters that we can note. Had there been a marked 

 diSerence between the character of the foliage in Series I — III we could 

 perhaps have found some such character as is discussed in Series III, 

 but there is not sufficient difference in this respect to make it discernible. 



Series IV. 



Plants from seed from Edinburgh and Dunbar, still in small pots. 

 These are markedly less infested and it was possible only to note them 

 as having either no scale at all, scale numbering from one to ten or scale 

 clearly exceeding ten on the whole plant. 



Edinburgh : 



Clean 20 



Under ten 18 



Over ten 16. 

 Dunbar, seed from healthy plants : 



Clean 17 



Under ten 8 



Over ten 5. 

 Dunbar, seed from diseased plants : 



Clean 10 



In this series also there is uneven distribution of Aleurodes and, 

 seeing that these plants had been kept side by side with the series in 

 larger pots which are more infested, it was suggested that the fly selected 

 for egg-laying those plants with more foliage or with healthy foliage not 

 likely to fall off. The plants as classed above for amount of Aleurodes 

 were then grouped according to the amount and condition of their 

 foliage, the resulting figures being: 



Clean plants Bad foliage 23 Good foliage 21 



Under ten plants ,, ,, 12 ,, ,, 24 



Over ten plants „ ,, 4 ,, „ 19 



