134 



ORaANOGEAPHY. 



because the stem then appears to pass through the leaf; or 

 when two leaves placed on opposite sides of the stem unite by 

 their bases they are said to be connate {fig. 259), as in the 

 Teasels (JD/psacus fidlonum and sylvestris) and some species of 

 Honeysuckle {Lonicera Caprifoliimi). 



2. Arrangement of Leaves on the Stem or Phyl- 

 i>0TAXY. — When only one leaf arises from a node, the leaves as 

 they succeed each other are placed alternately on different sides 

 of the stem, and are then said to be alternate {fig. 263). This 

 arrangement occurs in nearly all Monocotyledonous Plants, and 

 in the larger number of Dicotyledons also after the first two or 

 three nodes are developed. WTien two leaves are produced at a 

 node, they are usually placed on opposite sides of the stem, in 

 which case they are said to be opposite {fig. 261); or when 

 three or more leaves arise from the stem so as to be arranged 

 around it in the form of a circle, they are said to be verticillate 



Fig. 256. 



Fig. 258. 



Fig. 257 



1 



Fig. 259. 



Fig. 256. Sheathing leaf of a Grass. Fig. 257. Decurrent leaf of a species 



of Thistle. Fig. 258. Perfoliate leaf of a species of Hare's-ear (Bupleu- 



rum rotundifoUmn). Fig. 259. Connate leaves of a species of Honey- 

 suckle {Lonicera Caprifolium). 



or whorled {fig. 260), and each circle is termed a verticil or 

 whorl. When leaves are opposite, the pairs as they succeed 

 each other frequently cross at right angles, in which ease they 

 are said to decussate {fig. 261), and the arrangement is called 

 decussation. When different whorls succeed each other it also 



