THE COCOA BEAN VIEWED MICROSCOPICALLY. 947 



The cocoa beau is inclosed in a thin, brittle, reddish brown seed coat, 

 called the husk or shell. On the surface of the husk are often Found 

 numerous delicate, tubular cells, which come from the pulp of the fruit. 

 The important structures of the husk proper are the following: 



(1) The epidermal layer. 



(2) The loose parenchyma. 



(3) The fiber bundles with small spiral cells. 



(4) The layer of characteristic thick- walled cells. 



After softening the husk by soaking the beau in water, a portion of 

 the epidermal layer is readily torn away with the forceps, freed from 

 adhering fragments of the adjacent tissue, and placed on the slide for 

 examination. It is found to consist of a layer of moderately thick- 

 walled, somewhat elongated, irregularly polygonal cells (see Plate 

 XLVI). By careful dissection and careful manipulation of the light 

 and the micrometer screw, a layer of exceedingly delicate, transversely 

 elongated cells can be seen to lie directly under the layer just described, 

 but it is so very delicate that it is rarely seen in the examinations of 

 preparations of cocoa for adulterants, and is consequently of almost no 

 importance in such investigations. If some of the underlying tissue 

 exposed by the removal of the epidermis be transferred to a slide and 

 dissected apart, it will appear as a mass of loosely aggregated, rather 

 large, thin-walled, slightly elongated cells, those constituting the inner 

 layers containing a large amount of mucilaginous matter that swells 

 up in contact with water and ruptures them. This parenchymatous 

 tissue, which makes up the greater part of the husk, is pierced in all 

 directions by small, ramifying fiber bundles inclosing small spiral cells 

 and stone cells; near the inner surface of the husk it is interrupted by 

 a single layer of small, very thick- walled cells (see Plate XLVI), which 

 are very characteristic and withstand the disintegrating processes 

 of manufacture better than any other part of the husk. In fact, these 

 processes are often carried so far that it is only by very diligent search 

 that one is able to find any recognizable structures besides these cells 

 and the starch grains of the cotyledons. For the detection of the 

 presence of husks in cocoa preparations, these thick-walled cells are 

 first sought for; and after these the epidermal and parenchymal struc- 

 tures. The fiber bundles, with inclosed spiral cells, are not readily 

 distinguished from those of the cotyledon. 



If the brown husk be entirely removed from the remaining part of 

 the bean, a thin, transparent membrane will be observed, which partly 

 comes away with the husk and partly remains adherent to the bean 

 proper, dipping into all the clefts and plications of the latter. When 

 a portion of this membrane is examined with the microscope, it appears 

 as a single layer of small polygonal cells which are filled with granular 

 matter (see Plate XLVII). By careful manipulation one or more layers 

 of parenchymatous cells can be found underneath the layer just de- 

 scribed. Adherent to this membrane, especially to the folds entering 

 the clefts of the cotyledons, are numerous yellow, club-shaped masses 

 20393 No. 13 6 



