44 



by flies, especially Syrphidae, and small Hymenoptera. The 

 honey bee is abundant on some species of Brassica- Some 

 species are also visited by Lepidoptera. 



Brassica nigra Koch. Common mustard is a wayside 

 and garden weed. The yellow flowers are conspicuous, ar- 

 ranged in masses, and have a pleasant odor. It has four 

 nectar glands, two outside at the base of the petals and two 

 in front of the short stamens. The nectar occurs in large 

 drops on the glands where it is taken by the insect which in 

 doing so comes in contact with the pollen on both long and 

 short stamens, leaving some of the pollen on the capitate 

 stigma. In the absence of cross-pollination, self-pollination 

 occurs. 



Our violets are all early flowering and the only 

 Violaceae. ..,,,,. , . , 



species to be had durmg the summer is the 



Pansy ( Viola tricolor L). In the cultivated forms the 

 colors have been greatly changed. Three of the petals have 

 conspicuous pathfinders. The corolla is irregular, the lower 

 petal spurred at the base; stamens closely surround the 

 ovary, the two lower spurred. The spur acts as a nectar 

 gland while the lobed, hollow spur of the petal acts as a 

 receptacle. The insect thrusts its proboscis close under the 

 stigma into a hair-lined groove on the lower petal. The 

 anthers shed their pollen into this groove and thus the pro- 

 boscis becomes dusted with pollen. A small projection be- 

 low the stigma prevents the pollen on the insect from com- 

 ingr in contact with the sligma. As the insect goes to an- 

 other flower it leaves some of the pollen on the stigma. 



Of Viola pubescens. Ait. Robertson says: "This is 

 yellow with dark nectar-lines. The petaline spur is little 

 more than a gibbosity. The nectar-searching processes of the 



