10 MORPHOLOGY OP ANGIOSPERMS 



includes certain Pteridophytes among flowering plants. It is 

 certainly more in accord with present morphological concep- 

 tions not to limit too rigidly the possible origin of a structure, 

 and from this point of view it seems reasonable that floral leaves 

 in general may have been derived from contiguous structures 

 both above and below. 



It is not always easy to delimit a flower exactly from the 

 vegetative shoot, for there are numerous illustrations of grada- 

 tions between foliage and floral leaves ; but for all ordinary 

 purposes four different organs are readily recognized as enter- 

 ing into the structure of a highly developed flower. The dis- 

 carded doctrine of metamorphosis assumed that such a flower 

 is the type, from which all others are the modified descendants, 

 and this concej^tion is perpetuated in terminology. The same 

 conception dominates also in nearly all presentations of floral 

 diversities, as it is well-nigh impossible to abandon at once all 

 the terms of an obsolete conception and remain intelligible. 

 It has been a very prevalent conception, therefore, that flowers 

 of simpler structure than the assumed type are reduced forms. 

 There are certain cases in which this seems clear, as in the 

 relation of Lemna to the Araceae; but the vast majority of 

 simpler flowers are better regarded as primitive than as re- 

 duced forms. At present this is at least a valuable working 

 hypothesis, for it coincides in general with the morphological 

 and historical evidence concerning relationships, as well as 

 -with the doctrine of evolution. 



Accepting the evidence that the simpler flowers are for the 

 most part the more primitive forms rather than reduced ones, 

 certain prominent tendencies in the evolution of the flower, 

 admirably presented by Engler, may be discussed. It must be 

 understood, however, that only general tendencies are traced, 

 for the actual lines of descent can not be determined by our 

 present knowledge. 



The naked flower with one or more free sporophylls may 

 be regarded as the most primitive form. In fact, it is an 

 angiospermous flower without the characteristic floral leaves. 

 Such a flower may sometimes represent a case of reduction, 

 lint its persistent association with plants recognized as primi- 

 tive from other testimony is very strong evidence that it is a 

 primitive condition of the flower. From this stage a series 



