XX INTRODUCTION 



In position they are either radical, springing directly from an 

 underground stem, as in the Primrose j or cauline, produced higher 

 up, on an aerial stem. Both may occur on the same plant, as in 

 Tower Mustard (p. 39). 



In arrangement leaves may spring singly or scattered from the 

 stem, as in Balsam (p 105); opposite, in pairs, as in the Pink 

 (p. 69) ; or whor/ed, with more than two from one node, as in 

 Herb- Paris (p. 497). 



The veins of leaves may be paralld, as in grasses ; or curved, as 

 in the Lily-of-the- Valley, with much finer cross-veins ; or irregu- 

 larly net-veined, as in the Primrose, of very varying degrees of fine- 

 ness. They may be palmate, radiating from the base of the leaf, 

 as in the Sycamore ; or pinnate, with cross-veins springing from a 

 midrib, like the barbs of a feather, as in the Beech. 



The forms of leaves are very variable, and even on one plant 

 leaves may occur which can only be satisfactorily described by 

 uniting two of the following terms. 



They may be needle-shaped, as in the Pine ; linear, with parallel 

 sides and more than four times as long as they are broad, as in 

 the Grasses ; oblong, with parallel sides but not more than four 

 times as long as broad, as in some Pondweeds ; oval, with rounded 

 sides, widest across the middle and more than twice as long as 

 broad, as in the Butterwort; elliptical, less than twice as long as 

 they are broad, as in the Apple ; round, as in the Water-lilies and 

 Pennyworts ; lanceolate, widest near the base and at least four 

 times as long as they are broad ; ovate, or egg-shaped, widest near 

 the base but little more than twice as long as broad, as in the 

 Pear; kidney-shaped, broader than they are long, as in the 

 Ground-Ivy; ob-lanceolate, or reversedly lance-shaped, as in the 

 Ribwort Plantain (p. 403) ; obovate, or reversedly egg-shaped, as 

 in the Cowslip; deltoid, or nearly an equal-sided triangle, as in 

 the Orache ; arrow-shaped, as in the Arrow-head (p. 511); halberd- 

 shaped, with the barbs, or auricles, as they are called, pointing out- 

 wards, as in Sheep's Sorrel ; or rhomboid, as in the Birch. 



The base of the blade of the leaf may be wedge-shaped ; taper- 

 ing downwards, as in the Daisy (p. 254) ; heart-shaped, as in the 

 Violet ; oblique, or larger on one side than on the other, as in the 

 Lime-tree (p. 97) ; decurrent, when it runs down the sides of the 

 stem as a wing, as in Thistles ; perfoliate (from the Latin per, 

 through, and folium, a leaf), when the auricles are so united 

 round the stem that the stem appears to be growing through the 

 leaf as in Hare's-ear (p. 202); ox peltate (from the Latin pelta, a 

 shield), when they are so united in a stalked leaf that the stalk is 

 attached to the leaf near its centre, as in the Pennyworts (pp. 174, 



