THE MICROSCOPE. 8i 



pieces is of a dark grey brown, while others are of a yellow brown 

 with no shade of grey present. The bark is frequently studded with 

 flattened protuberances of a lighter color than the surrounding 

 cork. 



The central part of the bark is much lighter colored and when 

 wet or freshly broken is of a peculiar blue-green color. 



The inner part of the bark is of a dark brown color and very 

 fibrous. It has a very strong disagreeable odor of opium when 

 broken into pieces. It is strongly acrimonious and produces a burn- 

 ing sensation in the mouth and pharynx. 



Microscopical Structure. — The cork or outer bark (see figure i. 

 a) is composed of about fifteen rows of thin-walled, regular, 

 parenchymatous cells, brick shaped and arranged radially; i. e., the 

 length of the cell standing parallel with the radius. They are gen- 

 erally empty. 



The middle or green layer of the bark {b) is composed of thin- 

 walled, long, oval cells. In the longitudinal section they are ar- 

 ranged tangentially, /. <?., the longest diameter of the cell is at right 

 angles with the radius. They average about 1-250 of an inch in 

 length, and about one fourth as wide, containing clear white 

 chlorophyll bodies and dead protoplasm and chlorophyll. Occasion- 

 ally a crystal is found as if by accident. In the cross section the 

 cells are oval or round and of irregular sizes. Sometimes oil cells 

 are present. The cell walls themselves seem to have absorbed color- 

 ing matter, for they are not a clear white as is usually the case with 

 cellulose. 



The inner layer of the bark or the liber layer (^) constitutes the 

 principal part of the bark, frequently being four-fifths of the whole 

 bark. It is composed principally of regular parenchymatous cells of 

 nearly equal diameters, and with thin walls. These cells are quite 

 regular toward the inner surface of the bark and grow more ir- 

 regular toward the outer edge of this layer. Some of the cells show 

 pitted marks, which are deposits of cellulose on the cell walls. 



Bundles of liber fibres are arranged in concentric rings through 

 this part of the bark, hence its name liber layer. On a cross section 

 (see figure i, B) these fibres are composed of hexagonal cells with 

 very thick walls, having only a spot or a central line for an opening. 

 On a longitudinal section the fibres are frequently i-io of an inch in 

 length. It is these long cells of the liber fibre that gives the fibrous 



