Vlll INTRODUCTION. 



37. Leaves arc 



sessile, when the blade rests on the stem without the intervention of a petiole. 



amplexicaul or stem- clasping, when the sessile base of the blade clasps the stem 

 horizontally. 



perfoliate, when the baso of the blade not only clasps the stem, but closes round 

 it on the opposite side, so that the stem appears to pierce through the blade. 



decurrent, when the edges of the leaf are continued down the stem so as to form 

 raised lines or narrow appendages, called wings. 



sheathing, when the base of the blade, or of the more or less expanded petiole, 

 forms a vertical sheath round the stem for some distance above the node. 



38. Leaves and flowers are called radical, when inserted on a rhizome or stock, or 

 so close to the base of the stem as to appear to proceed from the root, rhizome, or 

 stock ; cauline, when inserted on a distinct stem. Radical leaves are rosulate when they 

 spread in a circle on the ground. 



39. Leaves are 



simple and entire, when the blade consists of a single piece, with the margin no- 

 where indented, simple being used in opposition to compound, entire in opposition to 

 dentate, lobed, or divided. 



ciliate, when bordered with thick hairs or fine hair-like teeth. 



dentate or toothed, when the margin is only cut a little way in, into what have 

 been compared to teeth. Such leaves are serrate, when the teeth are regular and 

 pointed like the teeth of a saw ; crenate, when regular and blunt or rounded (com- 

 pared to the battlements of a tower) ; serrulate, and crenulate, when the serratures or 

 crenatures are small ; sinuate, when the teeth are broad, not deep, and irregular (com- 

 pared to bays of the coast) ; wavy or undulate, when the edges are not fiat, but bent 

 up and down (compared to the waves of the sea) . 



lobed or cleft, when more deeply indented or divided, but so that the incisions do 

 not reach the midrib or petiole. The portions thus divided take the name of lobes. 

 When the lobes are narrow and very irregular, the leaves are said to be laciniate. The 

 spaces between the teeth or lobes are called sinuses. 



divided or dissected, when the incisions reach the midrib or petiole, but the parts 

 so divided off, called segments, do not separate from the petiole, even when the leaf 

 falls, without tearing. 



compound, when divided to the midrib or petiole, and the parts so divided off, 

 called leaflets, separate, at least at the fall of the leaf, from the petiole, as the whole 

 leaf does from the stem, without tearing. The common stalk upon which the leaflets 

 are inserted is called the common petiole or the rhachis ; the separate stalk of each leaflet 

 is a petiolule. 



40. Leaves are more or less marked by veins, which, starting from the stalk, diverge 

 or branch as the blade widens, and spread all over it more or less visibly. The prin- 

 cipal ones, when prominent, are often called ribs or nerves, the smaller branches only 

 then retaining the name of veins, or the latter are termed veinlets. The smaller veins 

 are often connected together like the meshes of a net, they are then said to anastomose, 

 and the leaf is said to be reticulate or net-veined. When one principal vein runs direct 

 from the stalk towards the summit of the leaf, it is called the midrib. When several 

 start from the stalk, diverge slightly without branching, and converge again towards 

 the summit, they are said to be parallel, although not mathematically so. When 3 or 

 5 or more ribs or nerves diverge from the base, the leaf is said to be %-nerved, 5-nerved, 

 etc., but if the lateral ones diverge from the midrib a little above the base, the leaf is 

 triplinerved, quintttplinerved, etc. The arrangement of the veins of a leaf is called 

 their venation. 



41. The Leaflets, Segments, Lobes, or Veins of leayes are 



pinnate (feathered), when there are several succeeding each other on each side of 

 the midrib or petiole, compared to the branches of a feather. A pinnately lobed or 

 divided leaf is called lyrate when the terminal lobe or segment is much larger and 

 broader than the lateral ones, compared, by a stretch of imagination, to a lyre ; run- 

 cinate, when the lateral lobes are curved backwards towards the base of the leaf ; 

 pectinate, when the lateral lobes are numerous, narrow, and regular, like the teeth of a 

 comb. 



