HAZELS 209 



furnished many varieties for importation into this 

 country. It is a species, however, with which our 

 plant breeders may work successfully with the ob- 

 ject of attaining size of nut, if that is desirable. 

 Some of my own hybrids between this and the 

 American hazel have small nuts. 



A number of species of European and Asiatic 

 hazels are cultivated extensively but without possess- 

 ing characteristics which are remarkable beyond 

 those mentioned in these notes. The cultivation of 

 foreign hazels in America made slow progress for 

 many years, although nuts were planted and nur- 

 series sent out seedling trees and layered stocks of 

 fine varieties to their customers. The reason for this 

 late development of the European hazel was due to 

 its vulnerability to the common hazel blight, Crypto- 

 sporella anomala. This blight attacks the trunk as 

 well as the smaller limbs of the introduced hazels. 

 It belongs to our common American hazel and does 

 little harm when growing upon that species, its at- 

 tacks being limited chiefly to bushes which have been 

 injured in some way. This doubtless presents a 

 parallel history to that of the Chinese chestnut with 

 its fungous parasite Endothia. Where host and pest 

 have developed side by side for ages the host, by 

 natural selection or by development of resistance, 

 does not allow the balance of nature to be disturbed. 

 The pest, however, when attacking species which 

 have not developed protection by way of natural se- 

 lection or by the development of resistance does 

 allow the balance of nature to be disturbed. The 



