68 



NORMAL AND EXPERIMENTAL POLLINATION. 



in the number of visits particularly occurred toward the end of the flowering 

 period, as shown in columns 5 and 6. The dominance of the species of 

 Osmia alternates in a striking and suggestive manner. A similar alternation 

 occurs in the case of Pseudomasaris and Clisodon, and the whole summary 

 shows the extent to which the maxima for different species tend to fall at 

 different times. The varying effectiveness of the genera is revealed by a 

 comparison of Bombus and Osmia; 2 individuals of the former visited 30 

 and 32 flowers respectively on the same days that those of Osmia averaged 

 but 2.5 visits each. 



Merritt (1897:19) found that Pentstemon palmeri, P. barbatus labrosus, 

 and P. bridgesi all have abundant nectar secreted by the bases of the two 

 upper stamens. The filaments of these curve inward to meet each other 

 and the other pair of filaments, and then rise to the upper wall. The 

 staminode crosses the tube above this junction and lies for the rest of its 

 length on the lower wall, thus excluding short-tongued visitors from the 

 nectaries. Dehiscence of the anthers is not simultaneous, and it is continued 

 for some time, the style lengthening only toward its close. The latter 

 lies against the upper side, but is curved to bring the stigma down to the 

 entrance, but out of the line of falling pollen. P. palmeri is constricted 

 in the tube where the 4 filaments meet about 4 mm. above the base, and the 

 sterile filament crosses just above this. The throat and limb are wide 

 enough to admit the largest bees. The anthers lie against the upper wall 

 and the heavily bearded staminode forces insects against them, though one 

 frequent guest, Osmia densa, appears to get nectar without touching them. 

 The vivid scarlet of P. barbatus labrosus stamps it as a humming-bird 

 flower. The anthers are exserted but protected by the upper lip, and serve 

 to guard the entrance, as the stigma does later. Honey-bees and Antho- 

 phora sometimes collect pollen from the anther-slits. In P. bridgesi honey- 

 bees attempted to reach the nectar, but in vain, while the pollen is dis- 

 charged too slowly to tempt bees. 



EXPERIMENTS. 

 CHANGE OF POSITION. 



Racemes inverted. — Table 50 gives a summary of the results of an 

 experiment in which 23 racemes in the normal position and 3 inverted 

 ones were under observation. 



Table 50. — Visitors to normal and inverted racemes. 



Specie3. 



Normal. 



Inverted. 



Relative No. 

 inverted. 



Osmia phaceliae 



bruneri 



Bombus juxtus 



Apis mellifica 



Pseudomasaris vespoides 

 Melissodes f remonti .... 

 Prosopis varifrons 



Total 



118 



