16 



STUDY OF NUTS MICROSCOPIC IDENTIFICATION. 



such an extent as to be easily removed by the pickers at the time of 

 harvesting. In the walnut groves of California no special machinery 

 is required to remove the outer pericarp, except where the nuts 

 have been sunburned or for some other reason have failed to develop 

 normally. 



Walnuts are further prepared by bleaching with a solution of 

 chlorid of lime, sodium carbonate, and a little sulphuric acid or 

 other bleaching agents. Polishing with soapstone is also resorted to 

 occasionally. 



Walnut varieties differ in hardiness, size of nuts, and thickness of 

 shell. The proportion of kernels varies, according to Colby, from 

 25.9 to 45 per cent. 1 Three fairly representative samples examined 

 by the writer contained, respectively, 40.8, 41.1, and 47.6 per cent 

 of kernels. 



FIG. 2. Persian walnut: A Epidermis of integument (X175); B Section of integu- 

 ment and superficial tissues of kernel (X175). 



Histology. The kernel of the Persian walnut has a fairly thick 

 integument which often separates easily from the meat. The outer 

 portion is quite sharply differentiated from the inner cell layers. 

 It consists of turgid cells varying in diameter up to 80 [A, but averag- 

 ing about 30 to 40 &A, which present a foamlike appearance (fig. 2, A). 

 Stomata occur at intervals in the epidermal layer. They are char- 

 acterized by thick reniform guard cells, quite regular in shape, almost 

 always fitting together squarely at the ends. Stomata measure 

 about 55 p in length by TO [i in breadth. The opening included by the 

 guard cells is also broader than it is long and usually has a sym- 

 metrical form. In a transverse section (see fig. 2, B) the outer tissue 

 is seen to have a thickness of 60 to 80 n and to consist in general of 



1 Colby. California Walnuts, Almonds, and Chestnuts. California Agr. Exper. Sta. Bui. 

 113, p. 4. 



