STRUCTURAL BOTANY. 81 



suits from the ripening of a peculiar sort of ament. The 

 terms strobile and cone are commonly applied to the fruit 

 of Conifers ; sometimes, however, also to that of the Hop, 

 Hop-Hornbeam, etc. 



IV. 



ARRANGEMENT OF LEAVES AND 



FLOWERS ON STEM AND 



BRANCHES. 



154. The several modes in which both leaves and 

 flowers are arranged on stem and. branches, have received 

 different names. 



A. PHYLLOTAXY. 



155. The term Phyllotaxy {ipvXXov, a leaf, and ra^iSj 

 order) denotes the arrangement of the leaves on stem and 

 branches. 



When they are found in pairs, threes, fours, etc., on the 

 same level or node, it does not usually occur to us, to in- 

 quire into the reason of such arrangement. But when 

 they are variously alternate, we are likely to ask, why they 

 are disix)sed in such or such oixier, and w^hich the physical 

 law may be, according to which this succession takes place. 



Here it may be observed, that the course of development 

 in the growing plant is universally spiral. 



150. As regards whorled leaves, including the oppo- 

 site, it must first be noted that the leaves of a whorl are 

 not placed directly above those of the whorl below, but at 

 some point perpendicular to the intervals between them. 



When the leaves are opposite, and each pair crosses at 

 right angles the next above or below it, the leaves will oc- 

 cupy four imaginary, equidistant, longitudinal or vertical 



