36 BOTANY 



at night, are white, and provided with a powerful scent so as to 

 attract night-flying moths and other insects. We shall later take 

 up some of the many cases of the adaptation of the parts of a 

 flower to these insect callers.^ Flowers adapted to be cross- 

 pollinated by insects are almost invariably irregular in shape. 

 Let us now consider rather in detail the structure of the sweet pea, 

 an example of such a flower. 



Sweet Pea. — The sepals are of almost the same size and shape; that is, 

 regular. The petals, however, are quite different from each other in form. If 

 you pull off the parts of the corolla you will find that they separate naturally 

 into a large expanded petal at the top of the flower; this is called the vane or 

 standard; two petals at the sides called the wings, and a curved part below 

 called the keel, the latter being made of two petals joined along the edge. 



A corolla of this kind is said to be 'papilionaceous from its fancied resem- 

 blance to a butterfly. What other plants do you know that have flowers of 

 this shape? 



If you press the point of a pencil down upon the keel of the flower, holding 

 it in a natural position, you will soon find that the point has taken up some 

 pollen. Evidentl}'' a bee might carry off pollen in the same manner. 



Now remove the corolla from one side of the flower so as to show the 

 stamens and pistil. Notice that the stamens are separated into two groups, 

 those in one group united by their filaments to each other. How many are 

 there in each group ? This condition of stamens is said to be diadelphous. 

 Draw the flower from the side, showing the above parts before j^ou pull off 

 the stamens. Look for the three parts of the pistil. Draw and label them. 

 Notice the little hairs covering parts of the pistil; can you imagine their use ? 

 In old flowers you can see that the ovary is forming the characteristic pod 

 of the pea family. 



Insects as Pollinating Agents. — We have seen in a general way 

 that insects assist in the cross-pollination of flowers. Let us now 

 turn our attention to the insects to see how in their structure and 

 habits they are adapted to play the important part that they fill 

 in the cross-pollination of flowers. No one who sees a hive of 

 bees with their wonderful communal life can fail to see that these 

 insects play a great part in the life of the flowers near the hive. 

 A famous observer named Sir John Lubbock tested bees and 

 wasps to see how many trips. they made daily from the hive to 

 the flowers, and found that the wasp went out on 116 visits 

 during a working day of 16 hours, while the bee made but a few 



^ At this point, at least one field trip should be introduced for the purpose of 

 studying under natural conditions tlie cross-pollination of flowers by insects. For 

 suggestions for such a trip, see Hunter and Valentine, Manual, page 207. Many 

 of the following exercises on fall flowers may profitably be taken in the field arid 

 reported on by the pupil as class exercises. Excellent suggestions for a field trip 

 may be found in Andrews, Botany All the Year Round. 



