BARBERRIES. 785 



to the stigma of another, the result of such cross-pollination being 

 greater vigor in the offspring. Thus Prof. Halsted * found that 

 barberry flowers from which insects had been carefully excluded 

 produced no fruit (others uncovered on neighboring branches 

 fruiting abundantly), and this in spite of the fact that through 

 jarring or as a result of age the stamens had curved inward as 

 far as they ever could. Microscopical examination showed a 

 considerable quantity of pollen to have been deposited among the 

 viscid hairs which form a ring about the top of the pistil (see 

 Fig. 3, H), but none whatever upon the cushion-like summit 

 which was found to be the only part that served as stigma. 



Barberry blossoms are great favorites among the insects. 

 Few of our June flowers gather about them a larger number of 

 bees, hornets, flies, butterflies, and beetles. The smaller bees and 

 certain flies are especially abundant. 



There is some reason to believe that the intense color of the 

 glands may serve as a guide to the insect, directing it at once 

 without loss of time to the nectar which collects in little hollows 

 between the bases of the filaments and the glands, where it is 

 held by capillary attraction. An insect in thrusting its proboscis 

 into a nectar cavity must touch the base of two filaments, where- 

 upon both stamens suddenly bend inward and strike the insect's 

 head. Now, Miiller f calls attention to the fact that while large 

 insects such as bumblebees pay no attention to this, but continue 

 to make the circuit of the flower, smaller ones, like the hive bee, 

 appear to be somewhat startled by this performance and fly away 

 at once to another barberry flower. But the insect carries with 

 it some pollen upon one side of its head, and if in the next flower 

 this comes into the same relative position as before, more pollen 

 will be added on the same part ; but if, on the other hand, the 

 flower is approached from the other side, then the pollen already 

 collected will be deposited upon the stigma, while at the same 

 time a new supply of pollen is being received which may in turn 

 be carried to still another flower. As the smaller insects are the 

 more common visitors, cross-pollination, which is so much the 

 best for offspring, must therefore be the most usual result. 



This sensitiveness of the stamens is exhibited by all the 

 species of Berberis so far as known, but is not found in other 

 members of the family, although a somewhat similar irritability 

 of stamens has been observed in certain of the Portulacacece,, 

 Tiliacem, Cistacece,, and Composites. The strikingly animal-like 

 nature of the movement is well shown by the following facts : A 

 chemical stimulus, such as ammonia gas, will induce contraction 

 as effectually as a mechanical stimulus. The presence of oxygen 



* Botanical Gazette, August, 1887, p. 201. f The Fertilization of Flowers, p. 91. 



VOL. XLV. 67 



