2. NORMAL AND EXPERIMENTAL POLLINATION. 



Treatment. — In the following treatment the species have been arranged 

 in general accordance with their phylogenetic sequence, beginning with 

 the buttercups and terminating with the mints. The discussion of each is 

 divided into two sections, the first dealing with normal pollination, the 

 second with experimental pollination. The experiments are considered 

 under four headings: (1) change of position; (2) mutilation; (3) artificial 

 and painted flowers ; (4) addition of honey and odor. Those that deal with 

 competition and constancy are reserved for the following chapter. Refer- 

 ences are given to the European and American observations on the pol- 

 lination of the same or related species, accompanied by a brief abstract 

 where it seems warranted. Each table or group of tables is summarized 

 in detail and a rSsume' of the general results is given at the end of the chapter. 

 These are further discussed in connection with the conclusions of other 

 investigators in the final resume 1 at the end of the fourth chapter. 



ACONITUM COLUMBIANUM. 

 NORMAL POLLINATION. 

 Structure. — The hood in Aconitum is formed of two colored sepals 

 united, the other two sepals making a landing-platform for insect visitors. 

 Two petals are modified into nectaries, while two form the sides of the hood. 

 The sepals and petals are colored alike, increasing the amount of color in 

 the flowers and making them more easily seen and attractive. The sepals 

 that constitute the landing-platform are smaller than the other sepals 

 and petals, but large enough to support the weight of the visitors. The 

 side petals arch above the stamens and protect them to some extent from 

 the rain, but do not interfere with the access of pollinators. However, 

 they hide the stamens from view when the flowers are seen from certain 

 positions. The nectaries are long and stalked, with a crested hood at 

 the top. To secure nectar, the visitors must have a proboscis 10 mm. 

 long in order to reach through the stalk to the hooded portion containing 

 the nectar (plate 2). 



Behavior. — The most frequent visitors to Aconitum are Bombus juxtus 

 and bifarius, of which the former is far more frequent, evidently because 

 this species is more numerous in the region. It is larger than bifarius 

 and covers more of the flower. It lands on the two lower sepals, with its 

 head toward the base of the nectaries, and the hind legs curve around the 

 small sepals, while the front pair grasp the side ones. The under part of 

 the thorax rubs back and forth against the anthers and stigmas as the bee 

 sucks nectar. It pushes the proboscis into both nectaries and often stops 

 to brush the pollen from its sides on to its legs, as it leaves the flower. 

 B. juxtus visits the flower for nectar, but in getting this, pollen is brushed from 

 its hairy thorax on the stigmas, and at the same time pollen is dusted on the 

 bee. When sucking nectar, the tip of the abdomen reaches to the three 

 styles. The bee scrapes pollen from its head parts as it leaves the flower. 

 It usually goes from the lower flowers on the raceme to the upper ones 

 and then down again. 



15 



