Ch. VI, 11] MORPHOLOGY OP CLUSTERS 339 



stamens and often also their pistils in so doing ; while simul- 

 taneously all of the interior flowers (the disk flowers) 

 remain comparatively inconspicuous and devoted entirely 

 to pollination. So far, indeed, does the resemblance to 



Fig. 237. — Flower cluster of Hydrangea Bretschneideri, a compound 

 corymb with showy neutral flowers. 



Lower left ; certain details of the fruit. (From Bailey.) 



large single flowers proceed that even a calyx-like structure 

 (called involucre) is developed from bracts, these coUective 

 features giving the clusters so much the aspect of single 

 flowers that they are popularly thought to be so. The resem- 

 blance, indeed, appeals even to insects, which visit and 



