CHAPTER XX 

 PARTICULAR FORMS OF FLOWERS 



270. GENERAL FORMS. Flowers vary wonderfully in 

 size, form, color, and in shapes of the different parts. These 

 variations are characteristic of the species or kind of 

 plant. The most variable part is the corolla. In many 

 cases, the disguises of the parts are so great as to puzzle 

 botanists. Some of the special forms, notably in the 

 orchids, seem to have arisen as a means of adapting the 

 flower to pollination by particular kinds of insects. A few 

 well-marked forms are discussed below in order to illus- 

 trate how they may differ among themselves. 



271. When in doubt as to the parts of any flower, look 

 first for the pistils and stamens. Pistils may be told by 

 the ovary or young seed -case. Stamens may be told by the 

 pollen. If there is but one series in the floral envelope, 

 the flower is assumed to lack the corolla: it is apetalous 

 (257). The calyx, however, in such cases, may look like a 

 corolla, e. g., buckwheat, elm, sassafras, smartweed, knot- 

 weed (Fig. 193). The parts of flowers usually have a 

 numerical relation to each other, they are oftenest in 3's 

 or 5's or in multiples of these numbers. The pistil is 

 often an exception to this order, however, although its 

 compartments or carpels may follow the rule. Flowers on 

 the plan of 5 are said to be pentamerous ; those on the 

 plan of 3 are trimerous (merous is from Greek, signifying 

 " member " ) . In descriptive botanies these words are often 

 written 5 -merous and 3 -merous. 



272. The corolla often assumes very definite or distinct 

 forms when gamopetelous. It may have a long tube with 



(136) 



