AN INTRODUCTION TO PLANT BIOLOGY 77 



that of the bean plant is called the "standard" ; the two petals at 

 the sides of the flower are called the "wings" ; and the united and 

 twisted petals form the "keel," which lies between the "wings." In 

 a bud just about to open note how the largest petal ("standard") 

 incloses the others. 



Inside the coil of petals ("keel") are ten stamens and the pistil. 

 Look at a flower in its natural position on a plant and note that the 

 two side petals (the "wings") are the only ones on which a bee 

 could easily alight. If you have opportunity, watch bees visiting 

 bean flowers in the garden. Hold a flower by its stalk in the natural 

 position, and with a pencil press downward on the two side petals, 

 and carefully watch the end of the coiled petals ("keel") as you press. 

 Note how the stigma and part of the style appear when the side 

 petals are pressed, and disappear within the coiled petals when 

 released. Imagine how a bee could cause the same exposure of 

 the pistil when alighting on these petals. Hold these side petals 

 down so as to keep the style protruded and with a hand-lens examine 

 the stigma, and also notice rows of hairs along the style. 



Now, carefully uncoil the twisted petals and note how the style 

 and the ten stamens are inclosed by the coiled petals. The fila- 

 ments of nine of the stamens are joined together at their base. The 

 stamens are firmly fastened in place, but the style is not attached to 

 the spiral tube formed by the twisted petals. The stigma does not 

 touch the anthers, but the hairs just below the stigma brush over 

 the anthers, and some pollen-grains cling to them. 



The meaning of this remarkable apparatus is this : When 

 a bee alights on a bean flower the stigma and the upper part of 

 the style is pressed out, as we have seen, and pollen is brushed 

 on the bee's body by the hairs on the style. Then the bee 

 goes to another flower, and when its style touches the bee's 

 body the stigma will touch some pollen from the first flower ; 

 and at the same time the hairs of the style will brush on to 

 the bee some pollen from the second flower. And so, as the 

 bee goes from flower to flower, it will brush pollen-dust on 

 stigmas and get pollen-dust brushed out from the anthers 

 by the hairs on the styles below the stigmas. There is very 

 little chance that the stigma of a flower will get pollen- 

 dust from anthers in the same flower. This may sometimes 



