26 ROOT-KNOT AND ITS CONTROL. 



lapse when touched by the knife. These objects are the mature 

 females of the nematode Heterodera radicicola (Greef) Lliiller. Each 

 is capable of laying several hundred eggs, more than 500 having been 

 counted by the writer in one case where the nematode was still 

 actively laying eggs. 



EGG. 



The eggs (PI. I, figs. 1 and 2) are ellipsoidal bodies, sometimes 

 symmetrical, more often slightly curved, and therefore somewhat 

 kidney shaped. They are usually a little over twice as long as broad. 

 Out of 71 different lots of egg masses measured by the writer, repre- 

 senting nematodes from 63 different hosts, the length varied from 

 67 to 128 n and the width from 30 to 52.5 fi. The greatest ranges 

 observed in any one lot of eggs were 67 to 108 by 33 to 42 //, 88 to 

 128 by 33 to 44 fi, 81 to 112 by 33.5 to 40 u, and 84 to 119 by 35 to 

 52.5 pL. These represented in each case eggs from the same nema- 

 tode, showing how variable in size they may be. The average range 

 of all measurements was 85 to 98 by 34 to 40 fi with an absolute 

 average of more than 500 eggs measured of 92 by 38.4 p.. These 

 dimensions agree closely with those given by Miiller,^ who studied 

 this nematode in Germany, his figures being 94 by 38 ji. On the 

 other hand, Frank,^ also working in Germany, gives the figures as 

 80 by 40 /JL. Stone and Smith ^ give the length as 100 /x. 



When the writer first examined the eggs from different hosts he 

 thought that there might be a possibility of distinguishing different 

 races of the nematode by the variations in the size of the eggs, but 

 the variability in size, even among the eggs from the same nematode, 

 soon demonstrated that no results of value could be obtained in 

 this direction. It seemed to be true, however, that the smaller, 

 less strongly developed females often produce the smaller eggs. 

 Thus, a nematode situated near the surface of a root, where the 

 pressure was not so great, was often larger and had larger eggs, but 

 this rule has so many exceptions that it can not be considered as 

 being in any way general. 



The egg consists of a densely granular body in which a lighter 

 spot, the nucleus, can occasionally be seen, inclosed in a tough, elastic, 

 transparent coat, or shell, probably chitinous in nature. When the 

 mother nematode is so situated that she has plenty of room to de- 

 posit her eggs so that they are not laid with difiiculty, they usually 

 leave her body unsegmented. On the other hand, if the eggs as 

 they are laid are crowded together so that considerable force has to 

 be used to lay each egg, the oviposition is delayed and segmenta- 

 tion begins before the later eggs leave the body. Only exceptionally, 

 however, do the eggs develop so far as to contain fully developed 



1 Miiller. 1883. ' Frank, 1885. 3 Stone and Smith, 1898. 



217 



