- 



THE FLOWER 9 



spermous flowers, for in this chapter only certain of the broader 

 morphological features will be discussed. 



Any strict definition of a flower seems to be impossible. 

 That the morphological precursor of the angiospermous flower 

 was some such structure as the strobilus of Pteridophytes seems 

 reasonably clear. In fact, the strobilus is plainly continued 

 among the Angiosperms in spiral flowers and spirally arranged 

 members. The appearance of distinct floral leaves associated 

 with sporophylls, however, is characteristic of the higher An- 

 giosperms. If a flower is essentially a sporophyll or a set of 

 sporophylls, as the older definition insists, Pteridophytes must 

 be included among flowering plants. If, on the other hand, a 

 flower is characterized by floral leaves, many Angiosperms are 

 not flowering plants. In any event, the term flower is of indefi- 

 nite application, and is incapable of sharp definition. It is a 

 term of convenience among Angiosperms, where it also in- 

 cludes strobili. The attempt of the older morphology to estab- 

 lish a definite conception for a flower, and to force all of the 

 sporophyll-bearing structures of Seed-plants into this concep- 

 tion was exceedingly unfortunate. 



The development of floral leaves among Angiosperms seems 

 to be connected with the evolution of entomophily, which has 

 resulted in immense diversity in the details of floral structure, 

 but such details are quite foreign to the purpose of this book. 

 The origin of floral leaves, however, is a cpiestion that must 

 be considered. 



That all floral leaves are derived from sporophylls may be 

 said to be the current view, as stated by A. P. De Candolle in 

 1817, and by many subsequent writers, notably Celakovsky in 

 1896 and 1900. Goebel. however, in his recent Organogra- 

 phie der Pflanzen, claims that while in a large number of cases 

 floral leaves may be derived from sporophylls, as in Xymphaea, 

 etc., they are often derived from " bracts." For example, he 

 calls attention to certain anemones in which the involucre be- 

 comes the calyx and this in turn may become petaloid. In other 

 words, he claims a double origin for floral leaves, namely, spo- 

 rophylls and foliage leaves, and whichever their origin the 

 result is the same. It may be of interest to note that Goebel's 

 definition of a flower, a definition originally proposed by 

 Schleiden, is " a shoot beset with sporophylls," which of course 



