116 SEEDS. 



(59) Cacao Seeds. 



The seeds of Theobroma Cacao, Linn. (N.O. Sterculiacese). 



The seed-coats comprise four distinct layers : (1) An outer 

 layer (epidermis) composed of a single row of tabular cells 

 which, in surface view (te), are seen to be elongated in the same 

 direction ; they are polygonal and have straight, smooth walls. 

 To this layer there is almost always attached the inner epi- 

 dermis of the pericarp (end), the cells of which are narrow and 

 elongated ; they cross those of the epidermis of the seed-coat at 

 right angles or often obliquely. 



Below the epidermis of the seed-coat is a layer consisting 

 of several rows of parenchymatous cells, (pa, pi). In this 

 tissue there is a row of large mucilage cells and numerous 

 nbro-vascular bundles containing an abundance of small vessels. 



The third layer is a single row of small sclerenchymatous 

 cells (sc). In transverse section they resemble a horse-shoe, 

 whilst in surface view they are polygonal. 



Lastly there is a layer of varying thickness composed of 

 collapsed cells with thin brown walls. 



The endosperm, of which but little remains, consists of two 

 distinct layers of cells. The outer (ae) is a single row of rela- 

 tively large tabular cells, which, in surface view, are seen to be 

 polygonal. They contain crystals of fatty matter, often grouped 

 into little masses, and here and there crystals of calcium 

 oxalate. The inner layer (ai) is made up of very irregular cells 

 containing crystals of fat. It not only surrounds the kernel of 

 the seed but lines the folds of the cotyledons. 



The epidermis of the cotyledons is composed of polygonal 

 cells containing granules of brown pigment. It bears the very 

 remarkable hairs (p) shown in the illustration, but these often 

 break off, and are then to be found on the membrane (endos- 

 perm) which surrounds the seeds. 



The cells of the cotyledons (co) are polygonal and vary a 

 little in their contents. Sometimes they are filled with starch 

 and aleurone grains embedded in a fatty mass ; sometimes 

 acicular crystals or tufts of crystals are associated with fat and 

 protoplasm, whilst some cells contain a brown amorphous pig 

 ment known as cocoa-red. The starch grains are very small 

 some are simple, but many are compound, the aleurone grains 

 are rather smaller than the simple starch grains. 



The diagnostic characters of powdered cacao seeds are : - 



(a) The elongated polygonal cells of the epidermis of the 

 seed-coat, crossed by the narrower cells of the inner epidermis 

 of the pericarp. 



(b) The sclerenchymatous layer of the seed-coat. 



(c) The cells of the cotyledons, with small starch-grains, 

 fat crystals, etc., and the pigment-cells. 



(d) JL he remarkable hairs. 



