Meloidj4 



them back to the laboratory for examination. 



In the meantime, thoy had made quite a growth and had established quite 

 large root systems. On examination we could find no galling on the 

 roots whatever. When we went back to the tubers, there they were, as 

 heavily infested as ever, perhaps more so. In cutting those tubers, we 

 saw some small circular areas, not brown, having a kind of water-soaked 

 appearance. In those tubers we found adults, old adult females, eggs, 

 larvae, and all stages of development up to yoving egg laying adult fe- 

 males. Obviously those parasites were going through generation after 

 generation in the tissues of that plant. They were not escaping into 

 the soil to reinfect the roots. So, as is often the case, these early 

 investigators were right — both can occur and does occur, but whether the 

 one or the other occurs is not fortuitous. It depends entirely on the 

 character of the tissues in which the females are embedded. 



In the old days (I think of the old days as the ' 20' s, about the time when 

 I first began work in the Department of Agriculture.) it was the general 

 impression among everyone who was working on root-knot that the reason 

 these so-called resistant plants did not become infected was because the 

 larvae did not go into the roots. I know that Mr. Arzberger, who was 

 with the Division of nematology back in the days when I first joined it, 

 was at that time quite busily running sections of root tips to see if 

 there was any structural peculiarity in these root tips which might act 

 as a barrier to the entrance of the root-knot nematode larvae. Nothing 

 ever came of that work; nothing was ever oublished. I presume that he 

 did not find any. 



It was not until about I9U0 when Barrens published his paper which showed 

 that in his work just as many root-knot larvae went into the roots of 

 Crotolaria as went into the roots of a tomato plant, when the two had an 

 equal opportunity to become infected. Starting from there I have always 

 regarded Barron's work as quite an important one — one of the landmarks 

 in root-knot nematode inV^estigation, because it changed our thinking a 

 good deal. Howev-n-, I was not at the time quite convinced that that was 

 true of all plants. 



I am sure you could not question his results, because he had them well 

 documented. I knew the situation was true for marigolds, that is the 

 horticultural form of the species Tagetes e recta , but I had a suspicion 

 it was not true of all plants. I had at that time in the greenhouse a 

 pop-ulation of jf'oot-knot from alfalfa from the '/est. I took an alfalfa 

 root tip and a Lantana root tip, put them side-by-side, and surrounded 

 them v;ith large numbers of root-knot larvae of the population that 

 originally came from alfalfa. After about twenty-four hours, the 

 alfalfa root-tip looked like a porcupine's tail, there were so many 

 larvae trying to get in and partly sticking out. None had gone in the 

 Lantana root, l/ith repeated trials, the most I ever got into the root 

 tip of the Lantana was two. Judging by this example, at least, the 

 larvae of some of the root-knot nematodes do not go into the roots of 

 some plants. 



