240 IfMlSSONS WITH PLANTS 



with pollen from the short anthers. If, now, it 

 goes to 6, its head strikes the stigma of the sjiort 

 style and pollen is left there. In all this opera- 

 tion, the insect is no doubt wholly unconscious of 

 its work in carrying the pollen; it is only intent 

 upon the honey in the bottom of the flower- cup. 

 No doubt the pollen from the different kinds of 

 flowers becomes more or less mixed upon some 

 of the stigmas, but the foreign pollen only, as we 

 have seen (270a), is likely to be effective. 



277a. This difference in relative lengths of stamens and pistils 

 is eharaoteristio of many kinds of plants. Flowers like the poly- 

 anthus are said to be dimorphic ("two forms"). Other flowers 

 have, in addition, an intermediate length of organs, and are said to 

 be trimorphie. Dimorphic and trimorpMc flowers are also said to 

 be short-styled, long-styled and mid-styled. Such flowers, as a 

 class, are said to be heterostyled ; but Gray has proposed that 

 they be called heterogonons, since the polymorphism applies to the 

 stamens as well as the pistils. The pupil may examine such 

 plants as mayflower (epigsea), pickerel-weed or pontederia, oxalis, 

 partridge berry or mitehella, large-flowered flax or linum of the 

 gardens, buckwheat, and some of the loose-strifes or lythrums. The 

 whole subject is presented in Darwin's book, "Different Forms of 

 Flowers on Plants of the Same Species." 



278. We have already made out the structure 

 of the sweet pea (Obs. xxxviii., Figs. 201, 202). 

 We shall now watch how the bees visit the flower 

 (Fig. 230). The insect is after the nectar at the 

 base of the flower, and in order to secure it, the 

 bee alights upon the keel and forces its way in 



