THE ANATOMY AND AFFINITY OF DEPARIA MOORE1, HOOK. 843 



bands of small-celled phloem on its flattened sides. The pericycle is usually in con- 

 tact with the protoxylems at the ends of the xylem plate, and at those points 

 contains specially large cells which appear to possess mucilaginous contents. 



The Rachis. 



The typical rachis of a well-grown leaf is slender and unbranched. It is about 

 6 ins. long and tapers gradually from the base, which is somewhat distended and 

 may measure slightly over ^ in. in breadth. At the point of departure of the 

 pinnse it is usually about T ^ in. broad. Very occasionally it is branched near its 

 base, but one of the two branches thus formed is short and aborted. 



In transverse section the outline of the rachis is fairly regular and slightly 

 flattened antero-posteriorly. 



The dermal appendages are scales and hairs. The majority of the scales are 

 inserted on the lower side of the rachis ; the majority of the hairs occupy the upper 

 surface. In young and unexpanded leaves, scales are borne along the entire length 

 of the rachis, but when the leaf is full-grown the scales have, as a rule, been shed 

 from the upper part of the rachis, but the hairs universally persist. The scales 

 seem to differ in only one detail from those found around the leaf-bases on the axis, 

 namely, that whereas the bases of the scales found on the axis are composed of 

 colourless cells, the scales on the rachis are of a uniform golden-brown colour. 



There are both branched and unbranched hairs of very varying form, but, 

 doubtless, some of the types observed are merely development stages of others. 

 Each hair stands on a rather enlarged epidermal cell. The most typical forms are 

 depicted in fig. 20. The short unicellular hairs are never apparently glandular, 

 but the small apical cells of the long, tapering, unbranched hairs are usually of a 

 glandular nature. Unbranched hairs consisting of three or four stout cells are quite 

 common, but those do not taper, and their apical cells are seldom glandular. The 

 branched hairs are usually shorter than the unbranched forms, are curiously bent, 

 and are almost invariably glandular. Such a series as that represented in fig. 20 is 

 frequently seen in a single section of the rachis, there being, apparently, no definite 

 distribution of the various types of hair. 



In the leaf-base itself, the greater part of the ground tissue is, at maturity, 

 sclerotic (fig. 10). The peripheral zone is composed entirely of small sclerotic cells, 

 and any tissue which retains its original parenchymatous nature lies in a central 

 position. Parenchyma bulks more and more largely in the ground tissue as the 

 rachis is ascended, and the peripheral sclerotic zone is correspondingly reduced but 

 still remains conspicuous throughout the entire length of the rachis (figs. 9-5). 



The epidermal cells are firm and thick-walled, and, with the exception of those 

 which form the bases of hairs and scales, are universally small. Along the entire 

 length of the rachis, on both its right and left sides, is a slight ridge or lateral line 



