Flower buds and the directions of floral evolution 



Alfred Gundersen 



The comparison of the structure of flower buds with that of 

 adult flowers is an interesting study. Such characters as an in- 

 ferior ovary, an irregular or sympetalous corolla, or epipetalous 

 stamens are evidently modern improvements. All are relatively 

 less developed in the bud than in the adult flower. 



The drawings by Miss Maud Purdy illustrate the develop- 

 ment of various characters: 



1. Primulaceae — Primula obconica 



Style and stigma absent in bud, very distinct in adult 

 flower. 



2. Iridaceae — Crocus vernus 

 Ovary, from superior to inferior. 



3. Ericaceae — Rhododendron indicum 



Placentation, suggestion of change from parietal to axile. 



4. Portulacaceae — Portulaca grandiflora 



Placentation, suggestion of change from parietal to cen- 

 tral. Three placentae early detach from the walls. 

 Finally the united upper part withers, making ap- 

 parently three central or basal placentae. 



5. Apocynaceae — Vinca minor 



Stamens, from hypogynous to epipetalous. 



6. Cruciferae — Cheiranthus kewensis 

 Hamamelidaceae — Loropetalum chinense 



In the buds the petals have the ordinary ovate form; the 

 claw of the petal of Cheiranthus and the linear petal of 

 Loropetalum develop later. 



7. Gesneriaceae — Chirita lavandulacea 



Corolla from regular to irregular; in the bud the corolla 

 is nearly regular. 



8. Caprifoliaceae — Lonicera fragrantissima 



In the bud the united part of the corolla is a fourth or 

 less of the whole, in flower more than half. Similar 

 change is the rule among Sympetalae. 



That floral development in a general way suggests lines of 

 evolution cannot be doubted. Among recent summaries of evo- 

 lutionary directions of flowering plants are those by Diels in 



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