EELWORMS 549 



or galls on the part attacked, and largest when the root is the 

 part selected. Such galls vary much in size in different 

 species of plants. In a specimen of Impatiens Oliveri, grow- 

 ing in the temperate house at Kew, many hundreds of galls, 

 varying in size from a marble to that of a walnut, were present 

 on the root, caused by Heterodera radidcola (Nal.). On the 

 roots of tomatoes, cucumbers, etc., the knots or galls are usually 

 less than half an inch in diameter, whereas, so far as I have 

 observed, on the roots of vines, clover, etc., the galls formed 

 by the same organism are yet smaller. 



Eelworms are almost universally considered as doing a great 

 amount of injury to cultivated plants, and in all probability 

 such is the case, yet I have often wondered whether they are 

 always the primary cause of mischief. Experience has taught 

 me to always look for fungus mycelium when I cut an eelworm 

 gall, and I am rarely disappointed. When such fungus is 

 grown out it proves to be a species of Fusarium or Fusoma. 



The following is a recapitulation of the life history of 

 Heterodera, and the formation of its galls, as given by Stone 

 and Smith in their excellent treatise on Nematode Worms : 



' Young worms coming into the soil from previously affected 

 plants wander about until they find roots suitable for their 

 attacks. Aided by a spear-like organ in the head they force 

 their way into the younger portion of the root and embed 

 themselves in its tissue. This irritation of the tissues of the 

 plant causes an abnormal development of the root, consisting 

 in an increased production of cells, and a derangement of the 

 tissues from their natural arrangement. The worms increase 

 in length and much more in diameter, assuming a spindle and 

 then a club shape. The females continue this swelling pro- 

 cess until they have the shape of a gourd and a size just 

 visible to the eye. They are now mature, and having been 

 fertilised by the male previous to their maturity they produce 

 eggs which develop into the young worms of the next genera- 

 tion. The life period of the female is about six weeks. The 

 male worms do not remain in the swollen form, but about 

 after four weeks from entering the root they change again into 

 a slender worm-like form which enables them to move about 

 and seek the females, with which they copulate and then 

 perish. While the worms are developing, the abnormal 

 growth of the root continues and results in a gall-like swelling 

 or enlargement and such a disarrangement of the tissues that 

 the progress of the sap through the plant is hindered to an 



