508 THE AMERICAN NATURALIST [Vol. LII 



is usually, though not always, distinguishable at birth 

 because of its pink or gray color, and those that are green 

 at birth usually develop the gray or pink color within a 

 few days. This color of the immature male has not, T 

 believe, been recorded in the published descriptions of 

 the species, and it is not impossible that it is a character- 

 istic of certain parthenogenetic lines only. 



Miss Patch (1915) has described a pink variety of each 

 of the viviparous forms. I have never seen these in my 

 experiments, though thousands of individuals have been 

 examined, except in diseased animals which died shortly 

 after discovery. The immature pink aphids in my ex- 

 periments have all been males. The occurrence of pink 

 females is probably a characteristic of certain partheno- 

 genetic lines. 



In my experiments the potato has been exclusively 

 used as the host plant. These plants were reared in pots 

 and were covered with lantern globes closed at the top 

 with muslin. 



Experiments 



Relation of Wlnt/ed avid IV in (/less Forms to Each Other 

 Experiment 298. — Starting with sister individuals, two 

 lines were bred for three generations, one line from ap- 

 terous parents exclusively, the other from alate parents 

 only. As in the other experiments to be described, about 

 a dozen adult females were placed together on a single 

 plant, to become parents of the following generation. 

 When they began to produce young, the latter were re- 

 moved daily, or every two days, to young plants. Suc- 

 cessive groups of young were placed on one plant until 

 they seemed likely to become too crowded (usually not 

 over 150 per plant), after which a new plant was used. 

 As many as five plants were required in some cases to 

 receive the young of one lot of parents. In the tables 

 these plants are designated, in the columns headed "Host 

 Plant," as first, second, third, etc. As the young aphids 

 became adult they were removed and either used for 

 further breeding or destroyed. 



