ABBANGEMENT OF LEAVES 35 



and collapse. As a consequence the entire leaf droops or, as gardeners 

 say, it ' flags.' 



In hot dry summers many thin-leaved plants may be seen to ' flag ' 

 daring the day, although the roots may he well supplied with water, 

 and only recover their freshness in the cool of the evening, when the 

 transpiration current is not so great. This current of water from root 

 to leaves continues as long as ever a particle of moisture remains near 

 the roots. And it even continues for some time after plants and 

 flowers have been severed from the roots and placed in water. This 

 explains why in a cut state stems and flowers often last a long time 

 fresh in water. If the base of the stems is cut from time to time, and 

 under water if possible, the freshness may be extended for several days. 



AERANGBMBNT OP LEAVES 



Leaves are arranged upon the stem in definite order and may be 

 alternate — that is, one after the other with only one leaf to each joint 

 as shown in the Glossary, fig. 6 ; opposite, when there are two leaves 

 to each joint, one on each side and opposite each other (Glossary, fig. 

 45) ; whorled or verticillate, when more than two leaves spring from a 

 joint and form a circle (Glossary, fig. 116). In "the case of Pine-trees it 

 looks as if several leaves sprang from one joint, but such is really not 

 the case : they are single leaves on a branch the joints of which are 

 very close together. 



The blade of a leaf may be in one piece, when it is called simple, as 

 shown in the Glossary, figs. 4, 8, 10 &c. ; or cut up into separate 

 leaflets, when it is compound, as in figs. 17, 19, and 50 in the Glossary. 

 Simple leaves assume roundish, elliptic, oval, or linear shapes with 

 intermediate variations, and may be either sharp or blunt or slightly 

 notched or pointed at the apex. The margins may be entire, wavy, 

 serrate, toothed, lobed, or variously cut, and the base may- be prolonged 

 below the insertion of leaf-stalk, the lobes uniting and producing a 

 peltate or shield-like form, as in the Indian Cress (Tropseolum) shown 

 at fig. 79 in the Glossary. When the leaf-stalk (petiole) is absent the 

 leaf is sessile, and when stipules are absent a leaf is said to be exstipu- 

 late. When the lobes of a sessile leaf are produced downwards to 

 clasp the stem, leaves are said to be amplexicaul, as in fig. 8 of the 

 Glossary ; and if the lobes of opposite sessile leaves unite, they become 

 connate as in fig. 33 ; or if single and surrounding the stem perfoliate, 

 as in fig. 82. 



Compound leaves may have the component parts called ' leaflets ' 

 radiating from the end of the stalk, as in the Horse Chestnut, when they 



D 2 



