14 



THE VEGETATIVE ORGANS 



veins ; but the leaf is so fleshy that the veins are not easily 

 seen. Notice the arrangement of the leaves on the stem 

 and the way in which they are related one to another. 



Perform the following experiment : Tie one end of 

 a piece of thread round the base of a leaf ; then wind the 

 thread round the stem from right to left in such a way that 

 it touches the base of each leaf in turn as it ascends. 

 Eventually you will meet with a leaf standing vertically 

 above the one with which you began. Count the leaves 

 passed by the thread, omitting the first, and determine the 

 number of times the thread has passed round the stem. 

 Commonly you will find that the spiral goes 

 twice round the stem and touches five 

 leaves ; thus we see that the leaves are 

 arranged spirally on the stem, and each is 

 separated from the one above or below it 

 by two-fifths of the circumference (Fig. 2). 

 Exceptions to this arrangement are not 

 uncommon in the Stock. The same test 

 might be applied to other plants, e. g. : 

 Groundsel, Oak, Deadnettle, Elder; and 

 Hazel. The arrangement of leaves on a 

 stem is called phyllotaxy (Gr. phyllon = 

 leaf, tasso = arrange), and is usually such 

 the leaves in a favourable position with 



iC^I 



Fig. 2. 

 Diagram of 



Leaf 

 Arrangement. 



as to place 

 regard to sunlight. 



The three structures root, stem, and leaf are con- 

 cerned with the growth of the plant, and are hence known 

 as vegetative organs. 



Reproductive organs. Eventually other organs, viz. 

 flowers (Fig. i,fl), appear on the upper part of the plant, 

 and these are concerned with reproduction. 



They are produced in considerable numbers both on the 

 main stem and on the axillary branches. These flowering 

 shoots form the inflorescence. Notice that in either 



