40 LABORATORY PRACTICE CHAP. Vlt 



3. Look at a branch from above and notice the number of 



vertical ranks. 



4. Make sketches. 



5. This is also an example of the cyclical arrangement. 



When there are more than two leaves arranged in a 

 circle about a node, it is said to be a whorl. 



IV. Examine a branch of some species of Begonia having 

 a conspicuous stem above ground. Notice : 



1 . The number of leaves at each node. 



2. The relative position of the leaves at two successive 



nodes. 



3. Draw a line from one leaf to the next, winding around 



the stem, and continue this line in a direct curve to 

 the next, and so on, until a leaf is reached directly 

 above (i.e. vertically) the one from which the line 

 starts. Notice : 



4. That this line is a spiral. 



5. The number of leaves through whose bases it passes be- 



fore it arrives at the leaf immediately above the one 

 from which we started. (In this we count the leaf at 

 which we start, but not the one at which we end.) 



6. The number of turns of the spiral. 



7. Make a sketch or diagram to show this spiral. 



8. The Begonia illustrates what is known as the spiral 



arrangement. (Compare it with the cyclical?) 



V. If we view the stem and leaves of the Begonia from 

 above, we shall see that the leaves are arranged not only in 

 this one spiral rank, but also in vertical ranks (see also II 

 and III, 3). Notice that, in this case, there are two vertical 

 ranks. For this reason such an arrangement as this is called 

 a two- ranked arrangement. 



