193 



thence excurrent, giving off numerous straight branches and 

 forming an oval or pyramidal, dense crown of foliage. 



The Z,eaves are a perfect exemplification of symmetry 

 and order. In arrangement they are in pairs, one leaf oppo- 



Fia. LIL JSsculus Hippocastanum. 



3, seed germinating. 



site another,* supported on long slender petioles. At top 

 the petiole divides, as in the Maple, into 7 veins diverging 



* The learner has already observed three modes of leaf -arrangement, viz., the 

 alternate in the Roseworts, etc., the opposite in the Maples, and the verticillate in the 

 Loosestrife. He will now be interested in comparing them. In the alternate arrange- 

 ment there is only one leaf at each node ; in the opposite, there are two, and in the 

 verticillate, 3 or more. The true nature of the alternate may be learned by an experi- 

 ment. Select a straight, leafy shoot or stem of an Apple-tree, Evening Primrose, or 

 any plant with seemingly scattered leaves. Beginning with the lowest leaf, fix a 

 thread to the base of the petiole. Pass then, right or left, to the next leaf above and 

 do the same ; thence to the next in the same direction, and so on by all the leaves to 

 the top. The thread will form a regular spiral. Let the same experiment be repeated 

 in a shoot with opposite leaves, and two spirals running parallel with each other will 

 be found ; and in the case of verticillate leaves, as many spirals as there are leaves in 

 each verticil. Hence the course of development in all growing plants is spiral. (See 

 Class- Book, pp. 46-50, on Phyllotaxy.) 



9 



