22 STUDY OF NUTS MICROSCOPIC IDENTIFICATION. 



which is strengthened by the fact that there are few places where the 

 tree appears to be indigenous. 1 



In microscopic structure, however, it appears to be quite distinct 

 from either. As it is the form more generally and widely distributed, 

 it is the one here described in detail (fig. 5, B). It resembles in form 

 the eastern black walnut, is smaller, as a rule, and is less pointed at 

 the base, with a nearly smooth shell marked by occasional small pro- 

 tuberances, especially along the sutures. The kernel is rather small, 

 and has a milder flavor than that of the eastern black walnut. 



/. calif ornica, only about half as large as /. hindsii, is very short 

 in proportion to its thickness, and has a smoother shell. AVoods and 

 Merrill 2 report 25.9 per cent of kernels. The sample examined by 

 the writer contained 27.5 per cent. 



Histology. The outer cells of the integument average 35 [/. in 

 diameter, rarely reaching 70 ^ in length (fig. 7, A). They are angu- 



A B 



FIG. 7. California black walnut : A Epidermis of integument showing coiled guard 

 cells (X175) ; B Section of integument and superficial tissues of kernel (X175). 



lar with somewhat wavy walls, and are, as a rule, slightly elongated. 

 The cell contents have a slightly opalescent appearance, suggest ing 

 those of /. nigra, but much less noticeable than those in that species. 

 Stomata are numerous and resemble those of the Japanese walnut 

 already described. The guard cells, however, are broader than in 

 that species, each one forming an almost perfect circle, so that the 

 entire structure has a breadth nearly twice as great as its length. 

 The usual dimensions of the stomata are 36 by 64 \L. It frequently 

 happens that the opposite ends of the guard cells are not quite in 

 contact, as a result of which a long, narrow transverse opening is 

 produced. The outer periderm tissue consists of a single layer of 

 cells 20 jjt. thick (fig. 7, B). The inner periderm is a layer of varying 



1 Smith, California Agr. Exper. Sta. Bui. 203, p. 27. 



2 Nuts as Food, Maine Agr. Exper. Sta. Bui. 54, p. 75. 



