496 



PLANT GROWTH AND PLANT COMMUNITIES 



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demonstrated in ontogenetic studies, the floral organs are truly homolo- 

 gous with the leaves formed during the vegetative phase (Figure 3). 

 But in the writer's view this classical concept can probably be applied 

 to all floral development, including even the most evolved gamopetal- 

 ous and epigynous types, as well as highly condensed and reduced 

 types. 



In floral inception and organogenesis, under the impact of a "flori- 

 genic" stimulus, important changes take place in the distribution and 

 quality of growth in the apex, both extrinsic and intrinsic factors being 

 involved. If, then, we begin with the prototypic flower, it is not diffi- 

 cult to see that certain characteristic changes in the distribution of 

 growth in the apex— i.^., in the vertical and transverse components- 

 could account for some of the major changes in floral construction: 

 e.g., hypogyny to epigyny, polypetaly to gamopetaly, etc. But within 

 any particular floral or inflorescence category {e.g., exemplifying 

 epigyny, zygomorphy, the umbel or capitulum type of inflorescence, 

 etc.) there is scope for great variation of detail: i.e., much of the evi- 

 dent floral diversity is of a minor rather than a major morphological 

 kind. 



In the transition from the vegetative to the floral phase, closely 

 comparable changes in apical growth and morphogenesis occur in 



LEAF 



BRACT 



SEPAL 



PETAL 



STAMEN 



STAMNOOUM 



CARPEL 



Figure 3. Camera lucida drawings of Aquilegia formosa var. trtincata, showing early 

 stages in the formation of leaves, bracts, and floral organs at the apical meristem. As 

 judged by the usual criteria — i.e., position and mode of inception — all these organs 

 are homologous. (After Tepfer, 1953.) 



