86 



ACADEMIC BOTANY. 



107) and Mint ; here the leaves are also Decussate (L. decusso, I cut 



across), each pair standing at a right 

 angle to the pair below it. Op- 

 posite leaves are Whorled (Verti- 

 cillate) when standing in threes, 

 fours, etc., on the same circum- 

 ferent line, as in the Woodruff 

 (Pig. 110) and Oleander. Al- 

 TBENATK leaves stand one above 

 another at regular angles on dif- 

 ferent circumferent lines, as in the 

 Sweet Gale (Fig. Ill), the Cherry, 

 etc. Alternate leaves are Fascicti- 

 late when bundled in twos, threes, 

 etc., as in the Pines; Rosulate 

 (rose-like) when separate but closely ar- 

 ranged, as in the House-Leek and Ply- 

 Trap (Fig. 112). 



182. Spiral Arrangement. — All leaves 

 have an established order of arrangement, 

 which is uniform in plants of the same species. 

 In the strictly Alternate arrangement, like that 

 of the Lime (in which the leaves stand above 

 one another on opposite sides of the stem), if 

 we fix a thread to the lowest node, or leaf-bud, 

 and wind it around the stem from node to node, 

 we shall form a spiral like the thread of a cork- 

 screw. Taking the first round as the expression 

 of the circumference or circle, 

 360°, the second node is half-way 

 round, 180° from the first; the 

 third is exactly above the first, 

 completing the circuit. This is 

 called the J cycle : 1 , the numer- 

 ator, names the number of cycles 

 or circuits; 2, the denominator, 

 names the number of nodes 

 passed in completing it. This 

 is also called Distichous^ or two- 

 ranked (Gr. dis, twice, stikos, 

 row). In the Sedges 3 nodes are 

 passed ; this is the | cycle, or Tris- 

 tichous. In the Cherry two cir- 

 cuits are made and five nodes 

 passed before the leaf (6th) 

 stands over the first ; this is the 

 ■J cycle, called Quincuncial (L. 

 quinque, five). Much more in- 

 tricate cycles are found in the 

 Plantain, House-Leek, and Pine 



Cone. ria. 112.— Fly-Xrap (Drosertt rotundifolia). 



183. The Leaf is the chief organ of digestion. It is an 



Fig. 111.— cf and ? 

 branches of Sweet Gale, 

 or Candleberry Myrtle 

 {Myrica Gaie) : a, scale of 

 catkin ; b, stamens ; 

 an anther. 



