60 THE MONTHLY BULLETIN. 



EELWORM PARASITES OF PLANTS.* 



By Peter Frandsen, Professor of Biology, University of Nevada. 



Earth, rich in decaying organic matter, sometimes swarms with 

 microscopic cylindrical worms, which, because of their wriggling move- 

 ments, are known as eelworms. The most of these feed upon decaying 

 substances and are probably beneficial in hastening the disintegration 

 of animal and vegetable matter so that it may again be available for 

 plant food. Certain forms have, however, acquired the habit of entering 

 the tissues of living plants, where they live as parasites, causing more 

 or less injury to their hosts. The parasitic species are distinguished 

 from the nonparasitic by the possession of a minute spear which can be 

 protruded from the mouth opening and enables the animal to make its 

 way into the roots and through the tissues of the plant. 



Among the parasitic forms the one known as Hcterodera radicicola is 

 becoming of increasing importance in this western country, because of its 

 wide distribution and the number of different kinds of cultivated plants 

 that it attacks. We now have records of some 500 species of plants 

 whi(3h are attacked, and these include the majority of truck garden 

 crops, alfalfa, clovers, some grains, a number of fruit trees and a host 

 of weeds. The presence of the parasite is indicated by the formation of 

 swellings on the roots and underground stems, which somew^hat resemble 

 the root bacteria nodules but are more irregular in shape and size, and 

 stand out less sharply from the rest of the root. A heavily infested 

 potato presents a characteristic appearance, one hard to describe but 

 readily recognized with experience. Its surface is marked by numerous 

 pimples, small warts, creases and ridges. On cutting across the tuber 

 one can see the mature females somewhat pear-shaped or circular in 

 cross section, about 1-25 inch in diameter, of a grayish white color, and 

 marked off from the tissues of the potato by a brownish ring. The 

 appearance of a heavily infested potato is not attractive to the house- 

 keeper and diminishes its selling value. There is considerable loss of 

 substance in paring, as the worms may penetrate to a depth of a quarter 

 of an inch, and the keeping qualities appear to be lessened. 



Each mature female is little more than a sac containing from 300 to 

 500 eggs, w^hich may undergo development inside her body. As the 

 eggs enlarge some of them are extruded. In from 20 to 28 days the 

 eggs hatch and the minute larvae, 1-70 inch long, emerge and, aided by 

 the decay of the tuber or roots in the soil, eventually make their way 

 into the ground and move about until they find a suitable root which is 

 entered, as a rule, from the tip. We have found that they also enter 

 the young potato tubers by way of the lenticels or breathing pores. 

 Several worms usually enter the same spot. After repeated moultings 

 the larvaB transform into mature males and females. The former are 

 elongated and cylindrical in shape while the latter become pear-shaped. 

 Mating occurs within the plant substance and the male then dies. It 

 requires about a month for the larvae to mature and the whole life 

 history' occupies from seven to eight weeks. 



♦Address before State Fruit Growrrs" Convention, Palo Alto, California, July 30, 

 1915. 



