126 



BOTANY. 



of the flower. Fig. 392 is the cross-section of Fig. 390, 

 and Fig. 391 gives a vertical section of the same flower. 



FIG. 389. 



FIG. 390. 



Are its parts arranged symmetrically ? that is, is the alter- 

 nation perfect ? 



You see that flowers present symmetry of arrangement 

 as well as symmetry of numbers, and it is important that 

 you should observe them in this respect. Determine what 



FIG. 391. 



FIG. 



parts of the flower you are studying alternate symmetri- 

 cally, and where the symmetry fails. You will often find 

 these observations valuable in classification. 



EXERCISE LIX. 

 Leaf-Arrangement. Phyllotaxis. 



To study leaf-arrangement, get straight leafy stems, or 

 shoots, a foot or more in length, such as are shown in 

 Fi g s - 393 an d 394, from any vigorous tree, shrub, or herb. 



