150 MORPHOLOGY OF THE ANGIOSPERMS 



longation of the "cross zone." The organ is considered fundamentally 

 tubular (peltate), even though it has a vascular core rather than a 

 central cavity. 



The distribution, orientation, and type of the lateral veins in the sta- 

 mens of some taxa have been considered proof that stamens are basically 

 diplophyllous in nature; the filaments in the Nymphaeaceae show some 

 vascular bundles that are inverted and amphicribral or bicollateral ( Fig. 

 55). But study of the complete vascular system of the stamens in the 

 Nymphaeaceae shows that the position, orientation, and type of these 

 bundles are the result of crowding and twisting as the broad ancestral 

 sporophyll is narrowed and, consequently, displaces the bundles. The in- 

 version of some of them is like the inversion of the sporangia which 

 have been shifted to the opposite side of the sporophyll. The inverted 

 bundles give no support to the theories of the peltate or diplophyllous 

 nature of the stamen. 



The presence, in some families, of organs transitional from stamen 

 to petal and the supposed, basically diplophyllous nature of both are 

 considered, under the diplophyllous theory, evidence that stamens 

 have been derived from petals. Support for this interpretation — the 

 reverse of the generally accepted theory — is found in the view that 

 simplicity of form is primitive, complexity advanced. That simplicity 

 may represent reduction from complexity is disregarded. 



The Telome Theory as Applied to the Stamen. Under this hypothesis, 

 the typical stamen is considered to represent, morphologically, a dichot- 

 omous system of telomes, with terminal sporangia greatly reduced and 

 compressed, and with only two distal dichotomies and their sporangia 

 surviving. Fascicles of stamens are seen to represent the survival of 

 several or many branchlets; the basal axis is greatly shortened, and the 

 distal tips are brought together in pairs. Support for this view is seen in 

 the side-by-side pairs of sporangia of the typical anther and in the 

 presence, in some fairly primitive orders — Dilleniales, Parietales, Mal- 

 vales — of a strong "trunk" vascular bundle which constitutes the central 

 axis of the telome system and supplies several or many stamens. 



The pairs of sporangia, characteristic of stamens, naturally suggest 

 dichotomies, and the pairing is perhaps even more prominent in the 

 laminar stamens where all the sporangia lie in one plane. (The two- 

 plane position of the sporangia in the typical anther has clearly been 

 derived from the one-plane position. ) The pairing of the microsporangia, 

 prominent in all stamens and especially in the primitive laminar types, 

 contrasts strongly with the basic, scattered position of the megaspo- 

 rangia. If the dichotomy of telomic structure persists in the sporophyll, 

 some similarity should be found in the megasporophyll. And it is per- 

 haps significant also that the outer member of each pair of sporangia is 



