152 ELEMENTARY STUDIES IN BOTANY 



93. The perianth. If the members of the perianth are 

 all alike in primitive flowers, they have not remained so in 

 most flowers. In general, they have become differentiated 

 into two very different sets (Figs. 101 and 108), the calyx and 

 the corolla ( 81, p. 131 ) . These sets differ not only in appear- 

 ance, but also in the use to which they are put. The sepals 

 (calyx) are usually leaf-like in texture and color, and protect 

 the more delicate inner members while in the bud condition. 

 The petals (corolla) are usually larger, more delicate in text- 

 ure, and not green, their color being called the color of the 

 flower. Such petals are associated in some way with the 

 visits of insects, which will be considered later. 



Almost every kind of exception to this general statement 

 can be found. For example, in the lily, the members of the 

 perianth are in two sets, but they are both petal-like in 

 texture and color, so that they can be distinguished only by 

 their relative positions (Fig. 123). In some flowers the petals 

 have disappeared, and the sepals may have the color and 

 texture of petals. Flowers without petals are said to be 

 apetalous (" without petals "). 



In spite of exceptions that may obscure the fact, the most 

 general tendency of flowers is to develop the perianth as two 

 distinct sets of members. 



94. Definite numbers. In the more primitive flowers, 

 the members are indefinite in number, for they are produced 

 upon a more or less elongated axis, as in a strobilus. In the 

 majority of flowers, however, this axis does not elongate, 

 but remains short and generally broadens at the tip. In 

 such cases, the flower members are produced upon this 

 broadened tip (receptacle), and cannot be indefinite in num- 

 ber, for the space is limited. As a consequence, they appear in 

 four circles, and each circle has a definite number of members. 



It is remarkable how constant the numbers are in the two 

 great groups of Angiosperms. In the Dicotyledons (87, 

 p. 146) with definite numbers, the prevailing number is five, 



