14 STUDY OF NUTS MICBOSCOPIC IDENTIFICATION. 



of which consists of a semihy aline layer of collapsed cells about 

 40 (A thick. The embryo has the same structure as the embryo in the 

 almond. The aleurone grains are rather irregular in shape and of a 

 granular appearance, varying in size up to 30 JJL in diameter. 



PRUNE KERNEL. 



(Prunus domestica L.) 



The kernel of the prune (fig. 1, E) bears a close resemblance in 

 form to that of the almond but is considerably smaller, averaging in 

 length scarcely more than one-half that of the latter. The hilum is 

 conspicuous as a winglike fold of the integument extending for a 

 short distance along the edge of the kernel at its base. The flavor 

 though somewhat bitter is milder than that of the peach or apricot, 

 owing no doubt to the smaller content of amygdalin. Although 

 prune pits are considerably smaller than those of the apricot, a sam- 

 ple examined by the writer contained 21.2 per cent of kernel, an 

 amount which compares favorably with the apricot. 



Histology. The seed coat of the prune resembles closely that of 

 the apricot. (PI. II, fig. 2.) The epidermal cells have thin walls 

 and vary in length up to 200 [A, averaging from 100 to 125 \L. The 

 stone cells vary from 40 to 150 ^ in length, averaging about 100 \j.. 

 Pores are present as in the stone cells of the apricot, but are less 

 numerous in the outer wall. The height of the cells is usually less 

 than the diameter, and in side view they present a low domelike 

 appearance, with a very thick outer wall. Although arranged in 

 much the same manner as in the apricot, they display a greater tend- 

 ency to grouping and especially to arrangement in rows. Inter- 

 cellular spaces are numerous and of large size, so that their effect in 

 hollowing the sides of the stone cells is very noticeable. As seen in 

 cross section (PI. II, fig. 1), the seed coat appears to be very thin, 

 usually not over 50 \L in thickness, with a brownish outer layer, a 

 lighter middle layer of collapsible looking cells, and a thin brown 

 inner layer. These tissues contain no crystals. No perisperm is 

 discernible, although the outer hyaline membrane of the endosperm 

 may be derived from the perisperm. The endosperm varies in thick- 

 ness within wide limits. Over the edges of the kernel it is but 25 pi 

 thick and composed of one or two layers of cells. In this form it 

 extends for a short distance over the sides of the kernel, where it 

 begins to thicken rapidly, reaching a thickness of 350 \L or more over 

 most of the lateral faces of the kernel. The inner endosperm cells 

 have a collapsed appearance. 



The epidermis of the cotyledons is about 10 to 15 ^ thick. The 

 cells are larger and more distinctly visible than those in the species 

 already described, reaching an extreme length of 100 \L and a width 



