PLANT ORGANS AND ORGANISMS 1 57 



two motions, the circular and the longitudinal, and its most common 

 modification is the circle. 



In the alternate arrangement there is but one leaf produced at 

 each node. Examples: Aconite, Magnolias. 



Opposite, when a pair of leaves is developed at each node, on 

 opposite sides of the stem. Examples: Mints, Lilac. 



Decussate, when the leaves are arranged in pairs successively along 

 the stem, at right angles to each other. Example: Thoroughwort. 



Whorled or Verticillate, when three or more form a circle about 

 the stem. Examples: Canada Lily and Culver's root. 



Fascicled or Tufted, when a cluster of leaves is borne from a single 

 node, as in the Larch and Pine. 



The spiral arrangement is said to be two-ranked, when the third 

 leaf is over the first, as in all Grasses; three-ranked, when the fourth 

 is over the first. Example: Sedges. The five-ranked arrangement 

 is the most common, and in this the sixth leaf is directly over the 

 first, two turns being made around the stem to reach it. Example : 

 Cherry, Apple, Peach, Oak and Willow, etc. As the distance be- 

 tween any two leaves is two-fifths of the circumference of the stem, 

 the five-ranked arrangement is expressed by the fraction %. In 

 the eight-ranked arrangement the ninth leaf stands over the first, 

 and three turns are required 

 to reach it, hence the fraction 

 % expresses it. Of the series 

 of fractions thus obtained, the 

 numerator represents the num- 

 ber of turns to complete a 



cycle, or to reach the leaf ^^ . f coupllcate 



which is directly over the first; pio 8l _ Three principal types of 

 the denominator, the number vernation. (Robbins.) 



of perpendicular rows on the 



stem, or the number of leaves, counting along the spiral, from any 

 one to the one directly above it. 



Vernation. Prefoliation or Vernation relates to the way in which 

 leaves are disposed in the bud. A study of the individual leaf 

 enables u to distinguish the following forms. When the apex is bent 

 inward toward the base, as in the leaf of the Tulip Tree,-it is said to be 



