166 FRUITS. 



(84) Vanilla Fruit. 



The fruit of Vanilla planifolia, Andrews (N.O. Orchideae). 

 A transverse section of the pericarp exhibits the following 

 structure : 



(1) An epidermis composed of a single row of flattened cells 

 covered with a rather thick cuticle. In surface view, these cells 

 are polygonal and either isodiametric or axially elongated ; 

 they have slightly thickened pitted walls, and contain octohe- 

 dral and prismatic crystals of calcium oxalate, together with 

 little rounded bodies also of calcareous nature. Here and there 

 a small stoma may be observed. 



(2) A hypoderma consisting of a single row of axially elon- 

 gated cells with thickened, pitted walls; some of these cells 

 also contain crystals of calcium oxalate. 



(3) A collenchymatous layer made up of two or three rows 

 of cells with smooth walls, which are thickened at the angles. 



(4) A tissue corresponding to the mesocarp ; this is composed 

 of large polygonal cells, with smooth or pitted walls, containing 

 traces of chlorophyll, sugar and oily protoplasm. In some 

 vanillas (Mexican) a parenchymatous tissue of strongly reticu- 

 lated cells is found in the outer part of the mesocarp, but in 

 others this tissue is represented by a few reticulate cells near 

 the bundles. In addition to octohedral crystals of calcium 

 oxalate the mesocarp contains a considerable quantity of very 

 large raphides either in isolated cells or in rows of cells placed 

 end to end. The bundles that traverse the mesocarp are com- 

 posed of spiral, annular or pitted vessels, together with bast 

 tissue, and are surrounded by fibrous cells with strongly thick- 

 ened, pitted walls. Towards the base of the fruit the paren- 

 chyma of the mesocarp exhibits lignification at various points. 



(5) An inner epidermis, the cells of which near the median 

 part of the carpellary leaf are prolonged into long, tubular 

 papillae containing protoplasm and globules of oil ; the latter 

 substance is also contained in the cavity of the fruit. 



In the placentae elongated, slightly lignined, pitted cells 

 occur. 



The seed exhibits the following layers : 



(1) An outer layer of radially elongated cells, with very thick, 

 brown walls ; the cavity of these cells has the shape of an 

 inverted T. In surface view the cavity appears linear, and the 

 walls very thick. 



(2) An inner layer composed of several rows of polygonal 

 cells. 



The embryo is made up of polygonal cells containing aleurone 

 grains and fixed oil. 



The diagnostic characters of powdered vanilla are : 



(a) The outer epidermis of the pericarp, with calcium 



oxalate crystals and small stomata. 



(b) The outer epidermis of the seed-coat., 



(c) The parenchymatous mesocarp with large raphides. 



(d) The reticulated cells. 



(c) The oily contents of the papilla and many of the cells 

 of the mesocarp. 



