634 SCALE-LEAVES, FOLIAGE-LEAVES, FLORAL-LEAVES. 



and of which the external ones travel towards the apex of the leaf in an 

 arch parallel to the margin, are termed curved (campylodromous). The lateral 

 strands which are usually so delicate that they cannot be recognized by the 

 naked eye always form spans, connecting the adjacent main strands trans- 

 versely. In the leaf of the May Lily {Maianthemum bifolium) depicted in 

 fig. 150 ^ the number of main strands is very large and the span-like laterals 

 are short. In the leaf of the Frogbit (Hydrocharis Morsus-rance, see fig. 150 -) 

 only five main strands traverse the leaf -blade, the connecting ties being 

 remarkably long and distinct. In Bananas and Scitaminese {Musa, Maranta, 

 Zingiber, Canna) the curved main strands look like arched laterals branching 

 ofi" from a single central strand, but on looking closer it becomes evident that 

 the thick rib traversing the centre of the leaf, like a keel, is not a single 

 main strand, but consists of many separate strands which are embedded in a 

 large-celled mass of tissue. These main strands are inclined one above the 

 other laterally away from the keel, travel towards the leaf-margin and there 

 curve up towards the apex. In bananas this bundle of separate strands, surrounded 

 by parenchyma, extends from the base to the apex ; in species of the genus 

 FitnJcia (see fig. 150*) only part way to the middle of the blade. 



When several distinct main strands enter the blade from the leaf-sheath or 

 leaf-stalk, running parallel to one another in a relatively wide area without 

 dividing and not converging until the actual leaf -apex is reached, they 

 are termed parallel (parallelodromous). Such an arrangement of strands is 

 found in many liliaceous plants, in orchids, rushes, sedges, and especially in the 

 thousands of diflerent grasses. The strands enter the blade either from a 

 broad sheath, as, for example, in Oryza clandestina (see fig. 150^), when their 

 separate nature can be easily recognized even at the base of the blade ; or 

 they enter by a sort of stalk on which the blade is inserted, as in bamboo 

 leaves (see fig. 150 ^), where the strands entering the base of the blade appear 

 bent like a knee. Parallel strands are usually of unequal thickness, the central 

 being almost always stronger and more vigorous than the lateral. But even 

 among the lateral, thicker and thinner often alternate in a manner definite for 

 each species. In the slender False Brome Grass (Brachypodium sylvaticum), 

 for example, from two to five weaker strands always appear between every 

 pair of stronger ones ; the weaker are often so exceedingly delicate that they 

 cannot be recognized by the naked eye. The unaided vision recognizes eleven 

 almost equally thick strands in the leaf of Oryza clandestina, represented in 

 natural size in fig. 150^; under a lens five more delicate strands are to be seen 

 between every pair of these. When lateral strands are present, connecting the 

 adjacent parallel main strands, they always take the form of transverse ties. 



Finally, we have here to consider that remarkable arrangement of strands 

 which is called fan-like (diadromous). A few separate main strands enter the 

 leaf-blade, divide up repeatedly into forked, straight-running branches, and the 

 ultimate twigs terminate at the upper margin of the leaf. This course of the 



