5IO Journal of Agriculture. [lo Aug., 1910. 



There is a certain polymorphism amongst the males, especially in size 

 and form ; smaller forms with mature reproductive organs exist. This may 

 be due to defective nutrition. In .some worms (Gordius) this polymorphism 

 is due to the parasitic stage lasting longer in some than in others. 



Effect of Changes in the Food Supply. 



Like many of the lower forms of life, nematodes tend to become vege- 

 tative when the supply of food is restricted. As was pointed out in the 

 article on the Onion Eel-worm in the March number of this Journal, all 

 the group are to a certain extent restricted in their choice of food, and, 

 when their natural nutriment is withheld and .something else substituted, 

 they become sluggish, for a time at least ^ reproduction may entirely cease 

 and many of the weaker forms die. They all become more attenuated in 

 form, the cuticle thinner and more transparent, and in many little node- 

 like swellings composed of rounded cells arranged in clumps make their 

 appearance here and there throughout the entire length of the worm ; after 

 the appearance of these swellings, death very soon ensues. 



Many of the embryos ne\er Ijecome fully developed sexually at all ; 

 they become quite as long, indeed longer, than the fully developed worm, 

 but they remain much thinner. The length of the potato worm was incor- 

 rectly given in the previous article as one-fiftieth of an inch. The sentence 

 ought to have read " the embryos are one-fiftieth of an inch in length, while 

 the adults are one-twentieth of an inch." The length, of course, depends 

 a good deal on the quantity and quality of the food supply. The non- 

 sexual forms, so often seen when food is restricted, frequently reach one- 

 fifteenth of an inch or more in length ; thev are always, however, more 

 attenuated in form. 



Advantages of Rotation. 

 The great death rate, the sluggishness of the survivors, the cessation of 

 reproduction, and the fact that many of the embryos never develop sexu- 

 ally, all point to the great advantages to be derived from changes in the 

 food supply, such as takes place when rotation of crops is practised. I 

 sowed onion .seed in soil badly infested with ])Otato eel-worm ; it germinated 

 freely, and the plants were not attacked at the end of two months. The 

 clean potatoes grown in the experimental plots at Bellarine showed the 

 same freedom from attack by the onion eel-worm, though the ground in 

 the neighbourhood of the plots was so badly infested that all the onion 

 plants were carried off by disease. 



Life History. 



The statements, that " The larvae only live in the earth where the 

 females shed their skin, make their way into the tubers and then become 

 citron shaped." " The males undergo a change, and after a period of rest 

 seek out the females," are quite erroneous, for worms of all ages are found 

 in the soil. Copulation takes place there and then the impregnated females 

 bore their way into the tubers where, by the maturation of the eggs, the 

 uterus becomes greatly distended, the worm finally becoming a rounded sac, 

 full of eggs. The accompanying micro-photograph shows a female worm 

 taken from a recently dug potato. It is interesting, showing, as it does, 

 the commencement of the distention of the worm by the maturing of the 

 eggs in the uterus. I have seldom found a sexually mature male in the 

 tissues of a potato. 



The usual life cycle of the potato worm is therefore quite simple. A 

 potato is planted with the female in the cystic or rounded form ; the death 



