34 TYPES OF VENATION [CH. 



curved lines and cross-connections, as in most Dicotyle- 

 dons e.g. Sallow, Maple, Poplar, Oak, &c. 



On closer examination, however, we find that several 

 different plans of distribution cau be made out in each of 

 these types, some of the commonest of which are the 

 following. 



In reticulately veined leaves the midrib or principal 

 axial strand, which runs through the centre of the leaf, is 

 usually distinct from the secondary ribs, and these occur 

 in two chief forms. In the Beech, Elm, Hornbeam, Chest- 

 nut, &c, the secondary veins run out from the midrib like 

 the plumes of a feather, and the type of venation is Pin- 

 nate ; but in Maples, Plane, Nasturtium, Currant, Mallow, 

 &c, several strong veins diverge as they enter the lamina 

 with the midrib, somewhat as do the fingers of an open 

 hand, and the venation is termed Palmate. 



In parallel venation, too, a distinction must be drawn 

 between the longitudinally parallel venation of Grasses, 

 Orchids, &c, where all the principal veins run parallel to 

 the midrib or nearly so, and the obliquely parallel vena- 

 tion of Musa, Ginger, Revenala, Elettaria and a number 

 of other tropical Monocotyledons, where the secondary 

 veins leave the midrib as in the pinnate type, and run in 

 obliquely parallel straight lines to the margin. 



The further course and mode of ending of the secondary 

 and tertiary veins in reticulately veined leaves give other 

 characters worth noting e.g. in Rhamnus Frangula, 

 P minus Mahaleb, Docks, &c, each secondary vein curves 

 upwards and inwards before reaching the margin and 

 forms an arched loop with the next one above (looped 

 venation) : in the Myrtle and Forget-me-not these loops are 

 so flat that the appearance of an infra-marginal vein is pro- 

 duced, owing to their junction and course along the edge. 



In the Cornels the lower secondary veins curve upwards 



