10 STUDY OF NUTS MICROSCOPIC IDENTIFICATION. 



transverse section these cells have a collapsed appearance. In some 

 nuts rosette crystals, presumably of calcium oxalate. are found in 

 cells of the tissue near the vascular bundles. 



The endodermis consists of polygonal cells averaging about 35 pi in 

 diameter but occasionally reaching an extreme length of 75 \L. The 

 cell wall is irregularly marked by beadlike thickenings. 



Closely adhering to the seed coat is a striated hyaline layer about 

 25 (JL in thickness, which is probably to be regarded as perisperm or 

 the remains of the nucellar tissue of the ovule. This lies next to a 

 single layer of aleurone cells, about 25 pi or a little more in thickness, 

 constituting the endosperm. A few cells may be found divided by 

 walls parallel to the surface of the kernel. In surface view the 

 endosperm is seen to consist of oblong or isodiametric quadrilateral 

 or polygonal cells, the form apparently varying to a certain extent 

 with the part of the kernel from which the tissue is taken. The cells 

 vary up to 75 \L in length by 35 [JL in width. 



The epidermis of the cotyledons consists of elongated cells, as in 

 the hard-shelled varieties described farther on, forming a layer not 

 more than 10 \L in thickness. The parenchyma cells which make up 

 the cotyledon tissue vary from the Irypodermal cells with a diameter 

 about twice as great as the epidermal cells to cells 40 to 50 pi in diame- 

 ter, which make up the central tissue. The walls are thin and inter- 

 cellular spaces very small. The cells contain oil and aleurone grains, 

 which usually have a roundish or oval form, but occasionally are 

 somewhat angular. Those measured varied in size up to 20 pi in 

 length. 



In the hard-shelled almond the epidermis of the integument con- 

 sists of thin-walled cells as in the soft-shelled variety, with a large 

 number of stone cells suggesting those of the pericarp, but having 

 thinner walls (PI. I, fig. 2). Their appearance has led some authors 

 to the erroneous opinion that they represent cells of the pericarp 

 clinging to the kernel. 1 Wittmack and Buckwald, however, consider 

 these stone cells to be mere fragments of an original complete layer 

 of similar cells, a large part of which has fallen away in the ripened 

 seed. 2 Godfrin reports a complete layer of cells and recognizes tAvo 

 classes, ovoidal, and less conspicuous, flattened cells. He falls into 

 the error, however, of considering the walls of the two classes of 

 cells to be equally thickened. 3 



The inner and lateral walls of the stone cells are marked by pores 

 which may be large or small, few or many, round or much elongated, 

 all these variations being sometimes found in a single nut. These cells 

 resemble in size the corresponding cells of the soft-shelled almond. 



1 Wittmack, L., and Buckwald, J., loc. cit., p. 589. 



2 Ibid., p. 587. 



Godfrin, loc. cit., pp. 146-147. 



