i8g 5 . AN EEL WORM DISEASE OF HOPS. 197 



up what remained an imperfectly understood phenomenon for more 

 than a quarter of a century. 



In conclusion, I wish to express my thanks to the Keeper of the 

 Botanical Department of the Natural History Museum and to Mr. 

 George Murray, for aid and for permission to work in the laboratory 

 of that institution. 



South-Eastern Agricultural College, J. Percival. 



Wye, Kent. 



EXPLANATION OF PLATE III. 



I. — a, Under, b upper surface of leaf from " nettle-headed hop," showing charac- 

 teristic curling of edges and puckering of veins. Natural size. 



II. — Transverse section of leaf, showing abnormal development of tissue at a 

 and b. Magnified forty times. 



III. — As in II., showing further growth of tissue at side of midrib. Magnified about 

 forty times. 



IV. — Transverse section of root, showing injured cortex and irregular growth at 

 points where Tylenchus devastatrix, Kiihn, appears. Natural size. 



V. — Radial longitudinal section of IV., showing Tylenchus devastatrix in cortex. 

 a, cork cambium ; b, cortex ; e, bast. Magnified. 



VI. — Hop rootlet, with attached females of Heterodera schachtii. Natural size. 

 VII. — Hop rootlets, with Heterodera schachtii females; (a), beneath epidermis; 



(b), exposed after breaking through epidermis. Magnified. 

 VIII. — a, Female of H. schachtii; b, the same after rupture of female under 

 cover-glass, showing eggs and larvae. Magnified. 



IX. — Eggs in different stages of development, and free young larvae of Heterodera 

 schachtii, showing exsertile mouth-spear. Magnified about 250 times. 



