53TG VEGETABLE ORGANOGRAPHY. 



number of two or more, upon the same horizontal plane 

 around the stem ; — the second comprehends those which 

 are always presented solitary on a horizontal section. 



When more than one leaf is found upon the same 

 plane, they are said to be Opposite when there are two 

 facing each other, and Verticillate when there are 

 several. It is customary to join to these two funda- 

 mental dispositions, those of Gemminate leaves; that 

 is to say, those which arise side by side ; but they are 

 always a degeneration from some other primordial dis- 

 position : thus, sometimes they are really alternate, 

 springing very near together, as in Solanum ; sometimes 

 they are verticillo-ternate leaves, one of which is acci- 

 dentally wanting ; sometimes portions of compound 

 leaves, which are taken for entire ones, &c. Of leaves 

 which spring upon the same horizontal plane, the oppo- 

 site and verticillate only can be regarded as the essential 

 dispositions. These two arrangements might be reduced 

 to only one, for opposite leaves are, in reality, but verti- 

 cils with two leaves. 



It is an universal law in Organography, and which 

 applies very particularly to this case, that the greater 

 the number of parts, the less regular they are : thus, 

 verticils with two leaves are the most constant of all ; 

 those with three, four, five, &c. are successively less so. 

 Now and then we find verticils of two leaves which take 

 three — as, for example, Lysimachia vulgaris ; or those 

 with three which take two, or four, &c. But when the 

 verticils of ten leaves are examined, we frequently see 

 them vary two or four above or below their usual num- 

 ber — for example, in Galium. These variations take 

 place, either in an individual of the same species, or in 

 the same individual at different ages and different 

 periods of its existence. 



Opposite leaves are almost always disposed in pairs, 



