323 



resulted in the death of all the Aphids within 24 hours. In the 

 second case, no colonies survived more than six days, and repro- 

 duction was very feeble. Natural colonies on both hosts flourished 

 meantime from late May to mid-Augast and the end of July 

 respectively. A. grossulariae has not been recorded from other 

 food- plants, but during June three instances were observed where 

 winged migrants established themselves on the flower-heads of 

 Campanula, the colonies persisting for two or three weeks. 



The conclusions suggested by the foregoing observations are that, 

 as pointed out by Theobald, A. grossulariae is probably identical with 

 A. viburni. The first migrant from Viburnum can form colonies either 

 on Viburnum, which is the natural host, or else on Ribes. The de- 

 scendants of the migrants to Viburnum can with difficulty be established 

 on currant, though the resulting colonies are not so strong as those 

 derived from an early migrant. The descendants of the migrants to 

 currant cannot be re-established on Viburnum. It seems as though 

 in two or three generations some change takes place in the currant form 

 which prevents it from flourishmg on guelder rose. One explanation is 

 that there is some change in the constitution of Viburnum, such as an 

 increase of tannins, and that the strain on this plant can gradually 

 adapt itself to altered conditions which the newly transferred currant- 

 reared stock cannot tolerate. Though Theobald has suggested that 

 A. grossulariae may be the alternating form of A. viburni, he has twice 

 failed to transfer the former to Viburnum. It is also possible that 

 A. grossulariae is not the natural summer form of A. viburni, but is 

 merely a casual pest of the currant. In the case of Aphids that have 

 a regular migration between two plants, the change is usually from 

 a woody-stemmed primary to a herbaceous secondary host, and if in 

 the case of A. viburni the currant should be found to be the normal 

 second host, it would be a remarkable exception to this rule. Possibly 

 the species has not yet adapted itself to the conditions of modern fruit- 

 growuig. In a natural state the Aphids are probably able to follow 

 the whole life-cycle on Viburnum, but the spread of the cultivated 

 currant has presented them with an increasing supply of alternative 

 food which induces a change that makes a return to Viburnum im- 

 possible. Whether sex-producing forms can arise from the currant 

 stock, and thence return to the guelder rose, is not known. Otherwise 

 the infestation of the currant must be regarded as an unfortunate 

 accident in the history of the species, which entails a waste of migrating 

 individuals upon a cultivated plant that might otherwise have 

 perpetuated themselves on the natural host. It is obvious that infested 

 Viburnum should not be allowed to exist in the neighbourhood of 

 currant bushes. 



Byars (L. p.) & Gilbert (W. W.). Soil Disinfection by Hot Water to 

 control the Root-knot Nematode and parasitic Soil Fungi. — Phyto- 

 patJwlogy, Baltimore, Md., ix, no. 1, January 1919, p. 49. 



Experiments made to disinfect small quantities of soil Infested 

 v.ith Heterodera radicicola by means of hot water are described. 

 When four-inch pots were immersed for 5 minutes in boiling water 

 all the Nematodes were killed. The same result was obtained by 

 the application of about 1 U.S. gal. of boiling water to eight-inch pote 



