i§95 AN EEL WORM DISEASE OF HOPS. 191 



at a later date he examined fresh specimens and males, and stated 

 them to be Heterodeva schachtii. Dr. Adolf Strubell, of Bonn Univer- 

 sity, who has monographed this species, and Dr. A. Voigt, kindly 

 examined examples, and reported to the same effect. Here, however, 

 it may be mentioned that, as with the Tylenchus, the specimens on the 

 hop-roots are considerably smaller than those occurring on other 

 plants, and attack rootlets much thinner than usual. The females 

 measured by Dr. de Man measured from 0-5 to o-6 mm. long (Dr. 

 Strubell's measurements on females from beetroot, etc., are o*8 to 

 1*03 mm.). Detached from the rootlets and examined with the micro- 

 scope, they are observed to be like a lemon in shape, white or brown 

 according to age, and too opaque for the contents to be seen clearly 

 (Plate, Fig. VIII., a). On pressing one between a cover-slip and 

 glass side, the eggs, numbering from 200 to 300, can be squeezed out 

 of the dead body-cavity (Plate, Fig. VIII., b). The eggs are some- 

 what bean-shaped (Plate, Figg. VIII. and IX.), about 0-096 to 

 o-ii mm. long (-gi^ of an inch), and about half as broad, and go 

 through their development in the body of the mother. The parasite 

 is viviparous, and it is not infrequent to obtain from the same female 

 both free completely formed larvae, and eggs only partially hatched. 



The larvae, which are eel- or TylencJms-like, leave the body-cavity 

 in which they develop, and, according to the researches of Kiihn, 

 Strubell, and others, wander but a short time in the soil, soon finding 

 their way to a fine root close at hand. Here they pierce the 

 epidermis by means of a comparatively large spike which they can 

 extrude from the mouth, and then wriggle their way into the soft 

 parenchyma surrounding the central bundle of the root. They then 

 come to rest after casting their skin, live upon the root-sap, and lose 

 their eelworm shape, becoming plumper in form. At this stage the 

 sexes are differentiated, and the females continue to swell and grow 

 beneath the epidermis, until the pressure is sufficient to lift up and 

 rupture the outer cell-layers of the root. In this manner they become 

 exposed, only the head remaining in the root-substance. The females 

 are never eel-like, nor do they move freely. The males develop from 

 the enlarged resting larvae by contraction of the contents of the latter 

 and subsequent formation of a new membrane. Although, as larvae, 

 they swell and lift up the soft tissue by which they are surrounded to 

 a considerable extent, they do not break through the epidermis like 

 the females, but, after assuming a Tylenchus- or eel-like shape within 

 the old case or cyst of larval-skin in the rootlet, they pierce their way 

 outward, and after fertilising the female they die. Their life is very 

 short — only four or five days — and thus casual observations of the 

 male are less frequent. 



The whole life-cycle of the parasite from the egg to the adult 

 condition occupies about four weeks, so that a large number of 

 generations are possible in a year. 



It is a matter of considerable interest to find two distinct species 



