22 MORPHOLOGY OF ANGIOSPERMS 



is probably not a hindrance to any form of pollination, and cer- 

 tainly prevents self-pollination. Cross-pollination by wind or by 

 insects, therefore, appears as an offset to the loss of any advantage 

 originally gained by the dioecious habit ; and the appearance of 

 monosporangiate individuals in any Angiosperm group does not 

 imply a tendency toward a more primitive or more advanced 

 condition. For example, the monosporangiate habit of poplars is 

 no more indicative of -a primitive condition than is the monospo- 

 rangiate habit of certain Compositae of an advanced condition. 

 The older morphologists considered the floral members as 

 morphologically leaves, and presented proofs which to them 

 seemed decisive, such as the leaf-like position and intergrading 

 of members, and various malformations, among which are the 

 so-called " reversions.' 7 This conclusion was controlled by the 

 prevailing doctrine of metamorphosis, and under its guidance 

 nothing seemed clearer than that stamens and carpels are trans- 

 formed leaves. . While sepals and petals may be regarded as 

 often leaves more or less modified to serve as floral envelopes, 

 and are not so different from leaves in structure and function 

 as to deserve a separate morphological category, the same claim 

 can not be made for stamens and carpels. They are very an- 

 cient structures, of uncertain origin, for it is quite as likely 

 that leaves are transformed sporophylls as that sporophylls are 

 transformed leaves. It is a rigid morphology, however, domi- 

 nated by the doctrine of - " types," that denies to an organ so 

 thoroughly established as the stamen of Angiosperms a mor- 

 phological individuality. One might almost as well deny to 

 the leaf itself a morphological individuality because it did riot 

 always exist as a distinct organ. Just how long an organ must 

 maintain its independence before it can be recognized as a 

 morphological unit is not easy to say, but stamens and carpels 

 seem to have earned the right. To call a stamen a modified 

 leaf is no more sound morphology than to call a sporangium 

 derived from a single superficial cell a modified trichome. The 

 cases of " reversion " cited are easily regarded as cases of re- 

 placement. Lateral members frequently replace one another, 

 but this does not mean that one is a transformation of the other. 

 For example, in 1889 Barber * observed a Nympliaea in which 



* BARBER, C. A. On a Change of Flowers to Tubers in Nymphaea Lotus, 

 var. monstrosa. Annals of Botany 4 : 105-116. pi. 5. 1889. 



