160 Elementary Biology. 



cells. In the second place the shape of the perianth leaves 

 differs markedly from that of the ordinary leaf type. We 

 cannot go into the discussion of the variation in the mor- 

 phology of the perianth leaves, but must content ourselves 

 with saying that their form is as various as their hue. In 

 the lily they do not present shapes differing much from the 

 tapering form assumed by the foliage leaves. 



The arrangement of leaves on the stem has been con- 

 sidered of some im- 



FIG. 80. FLORAL DIAGRAM OF Liltum. 



(Alien.) portance by botan- 



ists, and its value 

 cannot be exaggerated. 

 There can be no doubt 

 that primitively the 

 mode of arrangement 

 of the perianth leaves 

 and sporophylla on the 

 floral axis must have 

 shown some likeness to 

 the mode of arrange- 

 ment of leaves on the 

 ordinary branch, just 



,, I, a, 3, sepals ; /, I, 3 , 3,. petals ; ,, ., 2 , 3, ^ ^ arrangement Q f 



outer stamens ; 



2 ' 3 > car P els - the sporophylla in Sela- 



ginella resembles that of the foliage leaves in the same type. 

 Owing, however, to the great shortening and condensation 

 which the flower axis has undergone (compare the bulb), 

 the likeness has become in most cases completely oblite- 

 rated. We are compelled, therefore, to discuss the arrange- 

 ment of the floral leaves (anthotaxis) separately from that 

 of the foliage leaves (phyllotaxis). The methods of ar- 

 rangement in both cases may be very well studied in the 

 foliage or floral bud. 



The study of the relationships between flowers is greatly 

 aided by the use of what are known as floral diagrams. In 

 such a diagram the various perianth leaves and sporophylla 



