EXPLANATION OF THE PLATES. XX111 



that the disease in the first instance is most prone to attack the 

 tuber between the cuticle and spiral vessels. 



4. Section of a potatoe affected with dry gangrene, with a 

 cavity in its interior of the form of an irregular X. The mass 

 left in this case is principally starch. (Natural size.) 



5. Section of parsnip in the first stage of the disease. (Na- 

 tural size.) 



6. Mangel wurtzel. In this case the whole structure ap- 

 peared killed, and the malady is seen to progress from the spiral 

 vessels. (Natural size.) 



7. Cells of diseased potatoe empty of starch. (Magnified.) 



8. A section of healthy wild potatoe, showing the cells filled 

 with starch. (Magnified.) 



9. Starch with cellular tissue disorganized, and fungoid fibre 

 substituted. (Magnified.) 



10. Little aggregations of starch, which are to be seen occa. 

 sionally in diseased potates in little isolated masses. (Magnified.) 



PLATE VIII. 



APHIS VASTATOR. 

 All the figures are magnified. 



FIG. 1. The ovum immediately after exclusion, showing the 

 two eyes through the membrane. 



2. Young Aphis. 



3. Full-grown larva, with the antennae in the position it car- 

 ries them when on the march. 



4. Aphis vastalor in the pupa state. In this figure the anten- 

 nae are reflexed over the back, a position which the insect always 

 takes when feeding. 



5. Claw of the Aphis. 



6. Abdominal tubercle. 



7. Rostrum. 



