108 THE STORY OF THE PLANTS. 



bourhood. Hemp, for example, is a case of a 

 plant where such an arrangement already exists; 

 some plants are male only, while some are female. 

 Mistletoe and hops are other well-known in- 

 stances, which the reader should carefully ex- 

 amine for himself at the proper season. 



All these are fivefold flowers, and I have 

 brought them in here merely because one of the 

 earliest and simplest threefold flowers we are 

 going to consider has also this peculiarity of 

 separate sexes. This is the common arrowhead, 

 a plant that grows in watery ditches, and a capi- 



FIG. 20. I, male, and II, female flowers of arrowhead. 



tal example of the threefold type in its simpler 

 development. Each flower, whether male or fe- 

 male, has a green calyx of three small sepals, and 

 a white corolla of three much larger and some- 

 what papery petals (Fig. 20). But the male 

 flowers have in their centre an indefinite number 

 of clustering stamens ; while the female flowers 

 have an equally numerous set of tiny carpels. 

 The blossoms grow in whorls on the same stem, 

 the males above, the females beneath them. At 

 first sight you would think this a bad arrange- 

 ment, because you might fancy pollen from the 



