secondary vein arches (brochidodromous). The intercostal areas 

 demarcated by these secondary veins are moderately uniform in 

 their size and shape. Intersecondary veins of composite origin 

 from the coalescence of tertiary veins, although few in number 

 (2-7 per leaQ, may occur within the intercostal areas. Tntra- 

 marginal veins of secondary origin are absent from all leaves 

 examined. 



Slender tertiary veins arise at widely acute to slightly obtuse 

 angles (80-110°) along the inner and outer flanks of the 

 secondary veins. These tertiary veins ramify towards the midvein 

 and/ or transversely within the intercostal areas to form a 

 ramified, random reticulum of non-oriented, polygonal, tertiary 

 areoles. These tertiary areoles are further subdivided by ramified 

 fourth and fifth order veinlets into a random reticulum of many 

 moderately well developed and small, polygonal or quad- 

 rangular areoles. The mean number of freely terminating 

 veinlets ranges between 16-30 per mm^, with an overall mean of 

 22 per mm^ (Table 4). Veinlet terminations are typically 

 tracheoid with spiral or pitted secondary cell walls (Plate 38). 

 Tracheoidal idioblasts and fibrous sclereids were absent from all 

 leaf specimens examined. The marginal ultimate venation of 

 these leaves consists of second through fourth order, loop- 

 forming veins and veinlets, which promote the "festooned" 

 appearance of the overall venation patterns. 



epidermis: The epidermal cells of all leaves are polygonal in 

 surface view, with straight walls. Cells of the upper epidermis are 

 of uniform size but are consistently larger than those of the 

 lower epidermis. Cells of the lower epidermis, however, may 

 reveal a greater degree of size variation than those of the upper 

 epidermis. 



In all leaves, stomata are restricted to the lower surface and 

 are strictly of the paracytic type, with one pair of subsidiary cells 

 aligned parallel to the long axis of each stomate (Plate 37E, F). 

 Guard cell lengths do not exceed 25Mm in any of the stomata! 

 and mean stomatal density ranges between 156-203 per mm2,' 

 with an overall mean of 183 per mm2 (Table 5). Stomatal 

 frequency, calculated as the relative percentage of leaf surface 



305 



