206 



STRUCTURE AND VITAL PROCESSES OF PLANTS 



If we repeat the experiment with the thread, described on 



I. 



II. 



page 65, we shall see that those seemingly 

 irregular leaves are arranged ,on the stem 

 in spirals. With the help of the thread 

 it is also easy to find out how many turns 

 are necessary to get to a leaf which is 

 exactly above the first, and which of the 

 number of leaves it is. Thus we count 

 five leaves on two turns in the case of the 

 Jack tree, or in the Shoeflower; each leaf, 

 therefore, takes |^ of a turn or makes an 

 angle of 144° with its neighbouring leaf. 

 The arrangement of leaves is in this case 

 Fig. 191. -Spiral inser- denoted by the fraction |. Grasses and 

 tion of leaves. Each leaf Lilics liavc their Icaves generally in the 

 takes I of a turn in I, position ; Other coiiimon positions are those 



and ^ in II. 2 ^ -,,,.. 



represented by the fractions J and |. 



The stem of 

 Elephantopus 

 {Kan. Nela- 

 muccala) is so 

 short that the 

 leaves appear 

 to grow all 

 from one point. 

 Such leaves 

 are also ar- 

 ranged in spi- 

 rals; they form 

 what is called 

 a radical leaf- 

 rosette and 

 s h o w very 

 plainly that the leaves 

 so arranged allow one 

 another their due share 

 of light. 



Fig. 102. — Loaf-rosette of Elephantopus. 



