IN THE FIELD 197 



it forms yellow, waxy masses. On the disc in the centre of 

 each flower, you will notice five minute black bodies. Pull 

 these out with a pin. The small yellow bags which come 

 out with them are the pollen masses. The teacher should 

 see that every pupil finds the different structures. 



I will now pass around to you a number of insects which 

 have peculiar little bodies adhering to their feet, and I 

 wonder if any of you will be able to identify these little 

 bodies. Willie says they are the pollen masses of milk- 

 weeds, and that is just what they are. Where did the 

 insects get them ? I caught these insects on milkweed 

 flowers. What did they do there? Look into the little 

 hoods ; some of them are half full of honey, and we know 

 now what the insects were after. In searching for the 

 honey, they could not help stepping on the little black 

 bodies. They stick to the insects' feet, are pulled out with 

 the adhering pollen masses, and the pollen masses are 

 broken and stripped off on other flowers. The daivs of 

 insects are the only means by which the pollen of milkweed can 

 be transferred from one flower to another. This shows that 

 the milkweeds are highly specialized for insect-fertilization. 



Scientific investigators have found that it is impossible 

 for a milkweed flower to fertilize itself. Why could the 

 wind or the hairs and wings of insects not transfer this 

 pollen ? Place some fresh milkweed flowers where house 

 flies and ants can get at them, and observe what happens. 



Besides the common milkweed, which grows everywhere 

 in rich fields, several other species are not at all rare. The 

 most conspicuous one is the Butterfly Weed,*-4efepfa tube- 

 rosa. Its flowers are of a beautiful bright orange, and the 

 plant deserves to be cultivated. It has no milky juice. 



Another common form is the Swamp Milkweed, Asclepias 

 incarnata, of wet places, and with bright purple flowers. 

 Some milkweeds have greenish flowers, but all have their 



