Dit,yl:l| 



plant while it was low and near to the E-f'ound. We find a similsr situa- 

 tion with a weed which grows in sandy soil of Holland. Again, this 

 severe stiinting with no swelling and no dissolution of the middle lamel- 

 lae, and no nematodes in the tissues. Experimentally, it can be shown 

 that the trouble is a result of the presence of the stem nematodes on 

 the young plants. After a fe\j weeks, these plants will grow out rather 

 normally. 



Yellow lupine may show symptoms that look anything but being due to stem 

 nematodes, and yet the condition is caused by stem nematode attack. 

 There is stunting, bunching, and irregularity of the small leaflets, and 

 some mottling. It looks almost like a virus disease. This is a condi- 

 tion which can be introduced l:)y inoculating yellow lupine seedlings with 

 stem nematodes of various races. The inoculated plants never recover 

 from this condition. The stem nematode race from red clover attacks 

 yellow clover, but it causes the normal kind of symptoms. The nematodes 

 multiply in the tissues but never is the result a plant with the stunted 

 condition and irregularity of the leaflets. 



It seems that cases are never really clear cut in natixre, so if I say 

 that in all cases multiplication of the nematodes occur only vrhere there 

 is dissolution of the middle lamellae and normal symptoms 3 remember that 

 there may be a few exceptions. Thus, it seems that the race of stem 

 nematode from rye multiplies to a certain degree in peas, although it 

 certainly causes abnormal symptoms.'" 



The abnormal symptoms shown can be considered as different form of 

 resistance of the plants to stem nematodes. Also shown is that these 

 nematodes ha.ve different iafluences on the plant. The salivary secre- 

 tion of the nematodes may consist of different components. One may 

 dissolve the middle lamella of the plant cells, others may cause dis- 

 tortions, and so forth. It appears that even a very small amount of 

 that saliva can influence the tissue of the plant even at quite a dis- 

 tance from the location of the nematode. The dissolution of the middle 

 lamellae is always around the immediate vicinity of the nematodes in the 

 tissue. However, stunting and other symptoms may occur at some distance 

 away. For instance, strawberry plants attacked by a few stem nematodes 

 from rye or onions may have crinkling of the leaves even though the 

 nematodes are situated about two or three inches from these leaves. 



The nature of the symptoms can be used not only for host range studies 

 in differentiating the various nematode races, but also for selection of 

 resistant plants for breeding purposes. This is the present case vjith 

 red clover in Holland. Selection of resistajit red clover is based on 

 selection of plants which show necrosis. It is not the only foi'm of 

 resistance. There is a small percentage of red clover plants which do 

 not show any symptoms at al]., or show very slow development of symptoms. 



-;;- Editor's note: At this point the talk wns no lon;'nr breed largely on 

 discussion of materials illuntratcd with lantern slides. 



