36 STUDY OF NUTS MICROSCOPIC IDENTIFICATION. 



Upon examining sections of the seed coat a layer of clear tissue is 

 found adhering closely to the inner surface. This is readily seen to 

 be composed of two portions, an outer layer about 20 p. or less in 

 thickness and not distinguishable into cells, probably representing 

 the perisperm, and a much thicker inner layer, composed of two or 

 three layers of cells representing the endosperm. 



The embryo, which consists of parenchyma tissue lacking charac- 

 teristic structure, is filled with oil globules and aleurone grains. 

 The latter sometimes reach a length of 15 ji, but their usual size is 

 not more than half as great. 



KEY TO SPECIES OF NUTS. 



The writer has prepared the following key to facilitate the micro- 

 scopical identification of the species of nuts described in this paper. 

 It is meant to be suggestive only, and persons making use of it 

 should in all cases compare the material for identification, point by 

 point, with the description of the species indicated by the key; or, 

 better yet, with known material, if that can be obtained. 



I. Epidermis of periderm containing stomata. 



A. Stomata normal ; that is, ends of guard cells fitting squarely together. 



1. Outer tissue of integument consisting of one or two layers of cells, 



endosperm of one to three layers. 



a. Guard cells of stomata very broad, epidermal cells turgid and 



foanilike Juglans regia, p. 16. 



6. Guard cells narrower, sometimes one abortive; epidermal cells 



larger and more angular than in last Juglans cinerea, p. 37. 



c. Stomata smaller than in 6, nearly circular; guard cells rather 



narrow; sometimes approaching type B; epidermal cells 

 angular and clouded in appearance Juglans nigra, p. 19. 



d. Guard cells very broad ; epidermal cells angular and very small, 



usually about 20 /JL in diameter Juglans calif omica, p. 22. 



2. Outer tissue of integument consisting of two to four layers of cells; 



endosperm one layer of cells. 



a. Stomata nearly circular; guard cells narrow, one sometimes 

 abortive ; length of epidermal cells averages about 75 /A, which 

 is much greater than the width Hicoria pecan, p. 24. 



&. Stomata nearly circular but with thicker guard cells than the 

 last; epidermal cells not so elongated Hicoria ovata, p. 25. 



B. Stomata abnormal; that is, coiled nearly or quite into circles; outer 



tissue of integument consisting of a single cell layer. 



1. Guard cells narrow, much coiled so that opposite ends sometimes 



overlap; endosperm consisting of two or three cell layers. 



Juglans siel)oldiana, p. 20. 



2. Guard cells broader, not so completely coiled; usually single layer 



of endosperm cells Juglans californica hindsii, p. 22. 



II. Epidermis of periderm containing no stomata. 



A. Epidermis of periderm with papilla' usually developed into stone cells. 

 1. Stone cells not developed or some cells with slightly thickened walls. 

 Rosette crystals sometimes present. 



Amygdalus communis (soft-shelled), p. 9. 





