DETERIIINATE INFLORESCENCE. 



217 



and more or less elongated inflorescence which is irregularly branched 

 twice, thrice, or a greater number of times. 



400. A Thyrsus, or Thyrse, is a compact panicle of a pyramidal, oval, 

 or oblong outline ; such as the cluster of flowers of the Lilac and 

 Horsechestnut, a bunch of grapes, &c. 



401. Definite or Deterftiinate Inflorescence. In this class, the flowers 



all represent terminal buds (380). The primary axis is directly 

 teraiinated by a single flower-bud, as in Fig. 327, and its growth 

 is of course arrested. Here we have a solitary terminal flower. 

 Further growth can take place only by the development of secondary 

 axes from axillary buds. These may develop at once as peduncles, 

 or as leafy branches ; but they are in either case arrested, sooner or 

 later, by a flower-bud, just as the primary axis was (Fig. 328). If 

 further development ensues, it is by the production of branches of the 

 third order, from the axils of leaves or bracts on the branches of the 

 second order (Fig. 329) ; and so on. Hence this mode of inflo- 

 rescence is said to be definite or determinate, in contradistinction to 

 the indeterminate mode, already treated of, where the primary or 

 leading axes elongate indefinitely, or merely cease to grow from the 

 failure of nourishment, or some other extrinsic cause. The most 

 common and most regular cases of determinate inflorescence occur in 

 opposite-leaved plants, for obvious reasons ; and such are accordingly 

 chosen for the subjoined illustrations. But the Rose, Potentilla, and 

 Buttercup furnish familiar examples of the kind in alternate-leaved 

 plants. 



402. The determinate mode of inflorescence assumes forms which 

 may closely imitate those of the indeterminate kind, already de- 

 scribed, and with which tliey have been confounded. Wlien, for ex- 

 ample, all the secondary axes connected Avith the inflorescence are 

 arrested by terminal flowers, without any onward growth except 



FIG. 327 - 329. Diagrams of regular forms of determinate or centrifugal inflorescence. 



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