METHODS OF POLLINATION. 21 



the central figure shows that the ovary has two cells ; 

 the margins of the two carpels have met in the 

 middle ; ^ and the enlarged placentas are covered with 

 ovules.^ 



It is a very usual occurrence with conspicuous 

 flowers, constantly visited by insects, to have the pollen 

 ready to be taken away hefore, the stigmas are prepared 

 to receive it ; so that such flowers must be " crossed," 

 or they would set no seed, unless the pollen remains 

 in the flower long enough, i.e. until the stigmas are 

 mature. The former condition, we shall see, is what 

 occurs in Pelargo'nium. 



All the flowers thus far referred to have the parts 

 of each whorl exactly alike, and they are, therefore, 

 said to be Regular. Whenever this is the case, the 

 insects can visit the flower on any point of the circum- 

 ference, and the honey-glands are situated at regular 

 intervals, as in Plumla'go, or else the disc runs all 

 round the flower, as we have seen in Rhus. There are 

 a great number of flowers in which the corolla, 

 especially, is ^Irregular, in that the petals are not all 

 the same in size or shape. This is easily seen in the 

 flower of the Sweet-pea (Fig. 46), and of Polygalas 

 (Fig. 36), in which South Africa abounds. But as that 



^ This will be fully explained hereafter. 



^ Pupils should always be taught and encouraged to draw 

 diagrams of flowers. It is best to observe the flower when half 

 expanded, as it can then be seen how the sejials and petals overlap 

 one another, respectively. 



