TURNIP DISEASE. 73 



(293.) In subsequent chapters I shall prove that these 

 important facts have their analogies ; for I shall show that 

 the same disease is produced by the same insect in different 

 plants ; and also that other species may produce similar 

 disease in the plants on which they feed. 



(294.) With respect to the potatoe plant, I have here to 

 enforce that the winged creatures settle upon the larger or 

 more vigorous leaves first, and produce young ones, which 

 rapidly multiply. These suck the juices of the plant, 

 causing the plant to die locally. They also cause the 

 under-ground stem to rot at the collar, and thus effect the 

 destruction of the entire plant, by completely separating the 

 haulm from the roots. 



CHAPTER XIL 



TURNIP DISEASE. 



White turnjps, method of attack thereon (296, 297). Effects of the 

 attack (298 301). Spiral vessels (302, 303). Effluvia from rot 

 (304). Effects of time (305, 306). Fungi (307). Aphis bras- 

 sicae, description of, (309, 310); its habits (311, 312). Swede 

 turnip (316). Conclusion (318). 



(295.) BESIDES the potatoe the vastator attacks other 

 plants ; a fact which is important not only on account of 

 the value of the plants which are destroyed, but also as 

 showing that the same insect commits similar ravages on 

 other plants. 



4 



