38 IOWA ACADEMY OF SCIENCE 



second crop 98.1 ; for black loam underlaid with gravel, second crop 

 101.03 ; for alluvial soil, third crop 68.7. 



The flower consists of a green calyx of five pointed lobes ; and a purple 

 corolla of the following parts, an upper larger petal, known as the 

 standard, two lateral petals, the wings, the lower part known as the 

 keel consisting of two united petals. The keel contains the 10 diadel- 

 phous stamens, 9 forming a tube and one separate, and a single pistil 

 with a style curved upward. The lower flowers open first, and then 

 continue to open toward the apex. It requires from 6-8 days for all 

 of the flowers of a head to bloom. Sometimes as many as 40 flowers will 

 be in bloom at the same time. The position of the flower is upward 

 and it retains this position. The pollen grains are contained in the 

 anther and though somewhat variable as shown in another table are' 

 generally elliptical, .02-.04x.028-.068 mm. The flowers because of the 

 pleasant odor and large amount of nectar are attractive to insects. 

 The nectar is concealed in the base of the staminal tube, 9-10 mm. long, 

 which is formed by the fusion of the nine lower filaments and attached 

 to the claws of the petals. The upper free stamen lies on one side so 

 that the opening of the staminal tube permits the insect to get the 

 nectar. When an insect, like the bumble-bee, lights on the flower, it 

 holds on with its fore-legs to the wings which are attached to the keel. 

 Tiie pressure exerted depresses the keel and wings so that the stigma 

 and stamens protrude, the latter being somewhat shorter than the 

 pistil. The other two legs are supported by the other parts of the 

 head of the clover. The anthers dehisce and the pollen is left on the 

 upper side of the bee's head. The stigma receives the pollen from an- 

 other flower. Self-pollination can occur when the insect withdraws its 

 head. "When the bumble-bee leaves the flower the parts return to their 

 position because of the elasticity of the base of the keel and a small 

 dilated vescicular process at the base of the wings. Some of the pollen 

 collecting insects can also depress the keel. 



Insect Visitors. 



Observations on the insect visitors of clover have been made at Ames 

 for a number of years. We are indebted to Prof. Herbert Osborn for 

 a determination of insects found prior to 1898 and to Prof. H. E. 

 Summers for those found since that time. The insect visitors here 

 named include those recorded by Robertson for Carlinville, Illinois, 

 (marked C.) and those from Ames (marked A.). Arranged in groups 

 by orders, they are as follows : 



