124 



MORPHOLOGY OF THE ANGIOSPERMS 



missing sporangia are the outer members of the pairs of the ancestral 

 lamina, often smaller and nearer the edges of the lamina wings than 

 the others. Latrorse anthers also provide in their form — intermediate be- 

 tween laminar and extrorse or introrse — evidence to support the ex- 

 treme change in position of the two outer, smaller sporangia. Latrorse 

 dehiscence has commonly been recognized as more primitive than 



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Fig. 56. Diagrams of stamen structure. A, longitudinal sections of stamens showing 



stages in freeing of the anther sacs from the lamina; B, cross sections of anthers 



showing stages in the development of anther sacs by the reduction of the lateral 

 and connective tissues. 



extrorse and introrse. The morphologists of the nineteenth century 

 called it "normal"; the other types, specialized. In position on the 

 sporophyll, latrorse anthers provide the step between laminar and ex- 

 trorse or introrse; they are characteristics of many primitive families — 

 Ranunculaceae, Rosaceae, Butomaceae, Crassulaceae, Monimiaceae, Tro- 

 chodendraceae. 



In position on the sporophyll, the microsporangia of the typical 

 anther are submarginal; in the primitive stamens, they are laminar. Dis- 

 tribution of sporangia is much the same in micro- and megasporophylls, 



