MISCELLANEOUS NUTS. 27 



ropean species, C. avellana L. and C. pontica Koch. The American 

 species, C. americana Walt, and C. rostrata Ait., have not produced 

 cultivated varieties to a great extent and are of comparatively little 

 importance commercially, although both are worthy of special atten- 

 tion on account of the failure of most attempts to introduce the 

 European varieties in this country. These failures are due to the 

 hazel blight, a disease caused by the fungus Cryptospora anomola Pk. 

 This disease, although common on C. americana,, is not especially 

 injurious to that species, and doubtless could be prevented in the 

 European varieties by proper spraying. 



The proportion of kernels is given by Woods and Merrill J as 47.9 

 per cent, although the writer obtained but 37.5, 38.4, and 39.4 per 

 cent from three average commercial samples. 



Histology. The kernel of the hazelnut is covered by a rather thick 

 reddish-brown integument, to which usually adhere some of the cells 

 of the spongy endocarp. The latter have thin, brown walls, usually 

 much wrinkled and collapsed, which vary from 50 to 100 [i in diame- 

 ter. The epidermis of the spermoderm consists of angular cells of 

 variable shape with an average diameter in the variety examined of 25 

 to 30 [i and an extreme length of 72 ^ (PL II, fig. 5) . This is the most 

 characteristic tissue of the nut on account of the intercellular open- 

 ings, which pierce the cell layer and seem to take the place of stomata, 

 which are absent. These spaces, occasionally located at the angles 

 of the cells, but more frequently at intermediate points, are rounded 

 or elliptical in shape, in the latter case with the long axis at right 

 angles to the cell boundary. Though varying considerably in size, 

 they are seldom more than 20 \L in diameter and are sometimes repre- 

 sented merely by thickenings of the cell walls. They are rarely 

 absent. 



Underneath the epidermis is a thin layer of spongy parenchyma/ 

 which in surface view closely resembles the epidermis. The inter- 

 cellular spaces as well as the cells, however, are larger, and the latter 

 have a more rounded outline. This layer is succeeded by a tissue 

 formed of compressed cells of a light brown color, the outlines of 

 which are seldom discernible. 



The spermoderm is well supplied with vascular tissue in broad 

 bands, which start at the chalaza and pass in curved lines over the 

 top and sides of the nuts toward the hilum. Each band is composed 

 of a large number of vessels of the spiral and annular types, about 

 10 to 15 [JL in diameter. 



The endosperm comprises a layer about 15 to 25 \L thick, made up 

 usually of one or two cell layers. The epidermis of the cotyledons 

 is not more than 10 JJL thick and is composed of cells usually under 



!Loc. cit., p. 73. 



