78 



MORPHOLOGY OF THE ANGIOSPERMS 



positae, Cornaceae, and Euphorbiaceae with petaloid involucres or 

 modified outer flowers are well known. Similar "false flowers" occur in 

 many other families, as in the genera Leucadendron, Actinotis, Pimelea. 

 In Euphorbia, extreme reduction in flower number and flower structure 

 forms a highly specialized flowerlike inflorescence (Fig. 36A); a naked 

 pistillate flower is surrounded by staminate flowers, each reduced to a 

 single stamen; sterile, fused branches of the inflorescence form glands. 

 The outer, petaloid, ray flowers of the Compositae form a pseudocorolla. 

 Where these flowers are connate, as in the "cup Cosmos" the re- 

 semblance to a true corolla is close (Fig. 37). 



Fig. 37. Sketches of inflorescence of Cosmos sp., from left to right, a normal in- 

 florescence and two with corollas of ray flowers connate by margins, simulating a 

 sympetalous flower. ( Drawing by Elfricde Abbe. ) 



Groups of flowers — usually staminate — may be so closely associated 

 that it is difficult to determine the limits of a single flower, and the 

 "flower" description is made up of two or more flowers — Leitneria and 

 several genera of the Betulaceae. In these taxa, the staminate "flower" 

 is made up of a cluster of flowers, each consisting of several stamens, 

 the cluster subtended by an adnate bract. In CercidiphijIIum ( Fig. 146 ) , 

 the staminate flowers, each a cluster of stamens subtended by a petaloid 

 bract, form a compact flowerlike inflorescence. The pistillate inflores- 

 cence consists of carpels arranged like the staminate flowers. That each 

 carpel, subtended by its bract, constitutes a flower is evident from the 

 orientation of the carpels: the ventral margins appear abaxial. Inflores- 

 cences commonly described as flowers are those of Triglochin and 

 Potamogeton. In Triglochin, anatomy demonstrates that the "flower" 

 consists of a whorl of staminate flowers, separated by a whorl of bracts 

 from a whorl of pistillate flowers. The presence of bracts (not stami- 

 nodes) between the stamens and the carpels is in itself sufficient evi- 

 dence that this is not a true flower. The "flower" of Potamogeton, long 

 considered by a few students an inflorescence, is shown bv anatomy to 



