XV.] THE BRACKEN FERN. 445 



epidermis, enclosing a white groimd-subsiance, interrupted by 

 variously disposed bands, patches, and dots, some of which 

 are of the same dark-brown hue as the external zone, while 

 others are of a pale yellowish-brown. 



The dark-brown dots are scattered irregularly, but the 

 greater part of the dark-brown colour is gathered into two 

 narrow bands, which lie midway between the centre and 

 the circumference. Sometimes the ends of these bands are 

 united. Enclosed between these narrow, dark-brown bands 

 are, usually, two elongated, oval, yellowish-brown bands ; 

 and, outside them, lie a number of similarly coloured 

 patches, one of which is usually considerably longer than 

 the others. 



A longitudinal section shews that each of these patches 

 of colour answers to the transverse section of a band of 

 similar substance, which extends throughout the whole 

 length of the stem ; sometimes remaining distinct, some- 

 times giving off branches which run into adjacent bands, 

 and sometimes uniting altogether wath them. 



At a short distance below the apex of the stem, however, 

 the colour of all the bands fades away, and they are trace- 

 able into mere streaks, which finally disappear altogether in 

 the semi-transparent soft tissue which forms the growing 

 end of the stem. Submitted to microscopic examination, 

 the white ground-substance is seen to consist of large poly- 

 gonal cells, containing numerous starch granules ; this tissue 

 is called the ground-pare7ichyma. The circumferential zone 

 is formed of somewhat elongated cells, containing little or 

 no starch, the thick walls of which have acquired a dark- 

 brown colour. These cells constitute the hypodervia. The 

 dark-brown bands, on the other hand, consist of cells which 

 are so much elongated as almost to deserve the name of 

 fibres. Their walls are very thick, and of a deep-brown 



