Co2 SCALE-LEAVES, FOLIAGE-LEAVES, FLORAL-LEAVES. 



Lateral strands with radiate arrangement exhibit conditions quite similar 

 to those with a feather- like course. Frequently they are reticulate as in 

 geraniums and mallows, the Judas Tree {Gerds Siliquastrum), and many 

 Umbelliferse, as, for example, in the leaves of Hydrocotyle asiatica,, illustrated in 

 fig. 149^. In some water-lilies looped lateral strands are also observed, whilst 

 arched lateral strands are very characteristic of Melastomacese. In these Mela- 

 stomacefe (see fig. 149^') the lateral strands originate from the main strand at 

 the base of the leaf-blade, and travel towards the apex of the leaf in elegant, 

 sweeping arches parallel to the margin. Numerous cross strands, like ties, 

 connect the lateral strands with one another and with the primary one, giving 

 an extremely ornamental appearance to this class of leaf. The leaves of maples 

 exhibit lateral strands radiating towards the margin ; this is particularly well 

 shown in the Norway Maple (Acer 2JiC'ittnoides), the leaf of which is illus- 

 trated in fig. 149 ^-. Planes (Platanus) also have lateral strands running 

 towards the margin and tei-minating in the points of the leaf, but it is worthy 

 of remark that in some species the branching of the lateral strands from the 

 primary one does not take place immediately at the base of the blade, but 

 somewhat above it. A peculiar modification of lateral strands with a radiating 

 arrangement is observed in many so-called peltate leaves (see fig. 149 "). In 

 these leaves the blade is more or less circular, and is connected with the central 

 stalk as the cover of an umbrella with its stick. The strands radiate out in 

 all directions from the point of attachment of the stalk, and without close 

 investigation of tlie relations between sucli a leaf and its petiole, it is often 

 quite impossible to say which of the radiating strands is to be regarded as the 

 main one. This ai-rangement is found in most species of Pennywort (Hydro- 

 cotyle, cf. fig. 149^), in Nasturtiums, Ricinus, and Nelumbium; the last-men- 

 tioned plant has also this peculiarity, that its peltate leaves are somewhat 

 depressed in the centre like a bowl. 



Leaf -blades with several main strands offer far less variety than those with 

 only one. The margin is almost always entire, and they are generally elon- 

 gated. The most noticeable variations consist in the number of the main 

 strands which enter the base, in their varying thickness, and in the direction 

 which they take in the blade. We have also to consider whether they divide 

 like a fork, and whether the lateral nerves which they give off are developed 

 as cross-connections, or as a fine-meshed net-work. 



When the latter is the case, that is to say, when the main strands entering 

 separately into the blade, and ti-aveUing towards the apex of the leaf are 

 linked together by a net-work of lateral strands with angiilar meshes, they 

 are then said to be apical (acrodromous). The numerous broad-leaved species of 

 Plantain (Plantago), species of Hare's-ear (Bupleurum) belonging to the Umbel- 

 liferse, the leaf of one species of which (Bupleurum falcatum) is represented in 

 fig. 150 \ show apical main strands. In the loaf of the Hare's-ear the main 

 strands are crowded together in the narrow base of the blade, and tlie meshes 



