MORE MARRIAGE CUSTOMS. 117 



of separate sexes. This is the common arrow- 

 head, a plant that grows in watery ditches, and 

 a capital example of the threefold type in its 

 simpler development. Each flower, whether 

 male or female, has a green calyx of three small 

 sepals, and a white corolla of three much larger 

 and somewhat 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 



II 



FIG. 20. I. MALE, AND II, FEMALE FLOWEKS 

 OF ARROWHEAD. 



same stem, the males above, the females beneath 

 them* At first sight you would think this a bad 

 arrangement, because you might fancy pollen 

 from the males would certainly fall or blow out 

 upon the females beneath them. But the plant 

 prevents that catastrophe by a very simple 

 dodge, which we shall have occasion to notice 

 in many other parallel cases. The flowers open 

 from below upward ; thus the females mature 

 first, and are fertilised by insects which bring to 

 fliSm. pollen from other plants already rifled ; 

 later on the males follow suit, and their pollen 



