414 HETERODERA RADICICOLA. 



parts of Atrica is most probably clue to lack of observation or 

 of the publication of its presence in those countries. I have 

 personally found the parasite in many farming districts in each 

 of the four provinces of the Union. 



As regards its origin, Neal is of opinion that it is indigenous 

 to a large portion of the southern United States, and as evidence, 

 states that he has found it "in many places in Georgia and 

 Alabama where neither trees nor plants have been introduced 

 from other sections." 



The writer is also able to state that it is harboured by 

 indigenous vegetation in several places in Natal that have never 

 been under cultivation as far as knowledge goes. This might, 

 lead one to the opinion that the pest is also of ancient origin 

 in South Africa were it not for the fact that it is easily possible 

 in sandy soils for the eggs and larvae to be borne by wind and 

 water streams from infested land. Thus, once introduced into a 

 district, the parasite may be disseminated by natural means and 

 indigenous vegetation in virgin soil be attacked. 



Some Suggestions for the Control of Root " Knot " in 

 South Africa. 



The problem oi the control of Heterodera, as well as of other 

 nematode plant parasites, has engaged the attention of many able 

 agricultural biologists for the past thirty years, but unfortunately 

 their endeavours have not met with any marked measure of success. 

 Attempts to mitigate the ravages often consequent upon infesta- 

 tion on a basis compatible with economy have been especially 

 unsuccessful, and the writer has seen numerous large young 

 orchards situated upon infected but otherwise ideal land, rendered 

 almost valueless. 



As has been previously indicated, the young which constitute 

 the only stage in the life-historv which is passed in the soil, 

 unprotected bv the roots, is capable of withstanding only a limited 

 range of variability of conditions and will readily succumb if 

 these limits be exceeded. Attempts to eradicate the pest must, 

 be aimed at the larva. 



In America and elsewhere numerous experiments have been 

 carried out to destroy the parasites. It is exceptional that 

 nematode root parasites pass their free life at any great depth 

 in the soil. They may be especially abundant in the first ten 

 inches of soil, but they are seldom found at depths greater than 

 about sixteen inches below the surface. Consequently, to deal 

 adequately with the pest, it would only be necessary- to destroy 

 the parasite by treating the surface soil, but even this is a difficult 

 task. To effect this, it has been proposed to subject the larvae 

 to treatment by chemicals, steam, etc. These methods, even if 

 thev achieve their purpose with a substantial degree of success, 

 could scarcely be adopted on as extensive a scale as is often 

 required owing to prohibitive costs. Speaking generally, the 

 chemical and other artificial fertilisers employed in practice in 

 agriculture do not appear to have any direct effect. Lime, both 



