THE MICROSCOPY OF THE COFFEE FRUIT
How the beans may be examined under the microscope, and what is revealed—Structure of the berry, the green, and the roasted bean—The coffee leaf disease under the microscope—Value of microscopic analysis in detecting adulteration
The microscopy of coffee is, on the whole, more important to the planter than to the consumer and the dealer; while, on the other hand, the microscopy is of paramount importance to the consumer and the dealer as furnishing the best means of determining whether the product offered is adulterated or not. Also, from this standpoint, the microscopy of the plant is less important than that of the bean.
Fig. 331. Coffee (Coffea arabica). I—Cross-section of berry, natural size; Pk, outer pericarp; Mk, endocarp; Ek, spermoderm; Sa, hard endosperm; Sp, soft endosperm. II—Longitudinal section of berry, natural size; Dis, bordered disk; Se, remains of sepals; Em, embryo. III—Embryo, enlarged; cot, cotyledon; rad, radicle. (Tschirch and Oesterle.)
The Fruit and the Bean
The fruit, as stated in chapter XV, consists of two parts, each one containing a single seed, or bean. These beans are flattened laterally, so as to fit together, except in the following instances: in the peaberry, where one of the ovules never develops, the single ovule, having no pressure upon it, is spherical; in the rare instances where three seeds are found, the grains are angular.
The coffee bean with which the consumer is familiar is only a small part of the fruit. The fruit, which is the size of a small cherry, has, like the cherry, an outer fleshy portion called the pericarp. Beneath this is a part like tissue paper, spoken of technically as the parchment, but known scientifically as the endocarp. Next in position to this, and covering the seed, is the so-called spermoderm, which means the seed skin, referred to in the trade as the silver skin. Small portions of this silver skin are always to be found in the cleft of the coffee bean.
The coffee bean is the embryo and its food supply; the embryo is that part of the seed which, when supplied with food and moisture, develops into a new plant. The embryo of the coffee is very minute (Fig. 331, II, Em)[101]; and the greater part of the seed is taken up by the food supply, consisting of hard and soft endosperm (Fig. 331, I and II, Sa, Sp). The minute embryo consists of two small thick leaves, the cotyledons (Fig. 331, III, cot), a short stem, invisible in the undissected embryo, and a small root, the radicle (Fig. 331, III, rad).