262 



PLANT STRUCTURES 



FIG. 247. Diagram of crucifer 

 flower, showing the relations 

 of parts ; four sepals, four 

 petals, six stamens, and one 

 carpel with a false partition. 

 After WARMING. 



The most specialized large group in this alliance is 

 the mustard family (Crucifera), with twelve hundred 

 species, to which belong the mustards, cresses, shep- 

 herd's purse, peppergrass, radish, cabbage (Fig. 246), etc. 

 The sepals are four in two sets, the 

 petals four in one set, the stamens 

 six with two short ones in an outer 

 set and four long ones in an inner 

 set, and one carpel whose ovary be- 

 comes divided into two loculi by 

 what is called a "false partition" 

 (Figs. 246, C, 247), and usually be- 

 comes an elongated pod (Fig. 246, 

 A, B). This specialized structure 

 of the flower distinctly marks the 

 family, whose name is suggested 

 by the fact that the four spreading 



petals often form a Maltese cross (Fig. 246, A). The pecul- 

 iar stamen character, four long and two short stamens, is 

 called tetradynamous ("four strong"). 



140. Roses. This family (Rosacem) of one thousand 

 species is one of the best known and most useful groups of 

 the temperate regions. In it are such forms as Spircva, 

 five-finger (Poten- 

 tilla), strawberry 

 (Fragaria) (Figs. 

 191, 207), raspberry 

 (Fig. 248), and 

 blackberry (Ru- 

 bus), rose (Rosa), 

 hawthorn ( CratcB- 

 gus), apple, and 

 pear (Pirus) (Fig. 

 249), plum, cherry, 

 almond, and peach 

 (Primus). 



FIG. 248. The common raspberry: the figure to the 

 left showing flower-stalk, calyx, old stamens 

 (). and prominent receptacle, from which the 

 "fruit" (a cluster of small stone fruits, each 

 representing a carpel) has been removed. After 

 BAILEY, 



