Galls caused by the Stem Eelworm Tylenchus 

 millefolii 



the rachides of Achillea millefolium Linn. 



PLATE 77. 



Habitat of the Common Yarrow.— One of the most 

 plentiful of British wild plant.s, varying considerably in 

 size according to situation. It grows on waste ground, 

 meadows, hedge-banks, and roadsides. 



The Gall is Formed by the eelworms feeding upon the 

 interior of the rachis. 



Position.— On the rachis of the leaf 



Manner of Growth. — Separately ; glabrous ; spindle-shape 

 or irregular in outline. 



Colour. — Pale green. 



Average Dimension.s of a Mature Specimen. 

 Length, 17 mm.; girth, 15 mm. 



May be sought during the months of June, July, and August. 



The Growth is complete by the end of July. 



These galls are frequently found on the same leaves as those 

 attacked by Honiiomyia inillefolii Lw. The eelworms, however, 

 appear to confine their attacks principally to the rachis of the 

 leaf and not the leaflets. They are rare and very local. Where 

 there is a patch of Achillea inillefolium L, having many plants 

 attacked by both gall-makers, a similar patch not many yards 

 away will be quite free from them. On the opposite page five 

 only of the rachides show swellings, while many of the leaflets 

 are galled by H. inillefolii. An average-size gall may contain 

 from twenty to sixty eelworms. 



The illustration is of specimens gathered at Hastings by 

 the author. 



