121 



ice a thread-like proboscis may be thrust, 

 but a creeping insect cannot pass. 



In the snapdragon the two lips oi the 

 flower are tightly closed, the lower one 

 decidedly projecting. Any small inf.ect 

 reaching this lower lip as a natural land- 

 ing place finds no entrance. When the 

 bumblebee alights upon the lower lip, 

 however, his weight depresses it and he 

 forces his way in, and in passing to an- 

 other flower effects pollination. It is in- 

 teresting to note that after this first and 

 important visit the lips remain open and 

 other insects pass in freely, "being in- 

 vited," as some one has said, "to eat at 

 the second table." 



In most of the orchids there is a very 

 complete adaptation of the flower to its 

 insect, by which almost every insect ex- 

 cepting one special kind obtains nothing 

 for its visit. The nectar is usually in the 

 end of a long spur, and to obtain it the 

 head of the insect must just fit between 

 two sticky buttons to which the pollen- 

 masses are attached. The length of the 

 spur is nicely adjusted to the length of 

 the proboscis of the visiting insect, but 

 his head must also be of a certain breadth. 

 If an insect visits the flower with a pro- 

 boscis too short or too long, or a head 

 too broad or too narrow, its visit is un- 

 availing. The danger of such narrow 

 specialization is apparent in the case of 

 the orchids, for each plant is so depen- 

 dent upon a special insect that the dis- 

 appearance of the latter seriously en- 

 dangers the continued existence of the 

 former. 



Protective closure. — It has long been 

 noticed that certain flowers open only in 

 the evening, the evening primrose being 

 a conspicuous example. These flowers 

 are adapted to the visits of the night- 

 fliers, the moths, and about clusters of 

 evening primroses numerous large iiawk- 

 moths may be seen after sunset. During 

 the day the flowers are closed and safe 

 from the visits of any insect, but by open- 

 ing in the evening they are not only ready 

 for the visits of the night-fliers, but they 

 avoid the visits of most creeping insects. 



notably the ants, who are not abroad 

 after "the dew falls." 



Protection against grazing animals. 

 — Although we are considering the ways 

 by which creeping insects are checked in 

 their efforts to visit flowers, it seems per- 

 tinent to mention the more universal 

 danger which comes from grazing ani- 

 mals. If flowers were as attractive to 

 grazing animals as they are to insects 

 they would be in danger of wholesale de- 

 struction. It can be observed, however, 

 that these animals as a rule avoid the 

 flowers of a plant, although they may 

 strip off its leaves. It is believed that this 

 avoidance is due to the fact that in or 

 about the flower cluster there are usually 

 secreted bitter, sour, or nauseous sub- 

 stances, which grazing animals have 

 learned to avoid. It should not be im- 

 agined that these substances are there for 

 that purpose, but being there the result 

 is that the flowers are avoided. It is un- 

 known how generally true this is, and the 

 effectiveness of this method of protection 

 may have been exaggerated. Those who 

 can observe cattle, however, are in a posi- 

 tion to test them with the flowers of the 

 various plants they are known to eat, and 

 determine how far they avoid them. 



In conclusion, it may be of interest to 

 call attention to the great complexity of 

 relations existing among plants and ani- 

 mals by repeating Darwin's famous illus- 

 tration known as "Cats and Clover." In 

 a certain district in England he observed 

 that the clover was pollinated by the bum- 

 blebees, which had their nests in the 

 fields. It followed, therefore, that the 

 more the bumblebees, the more the 

 clover. He also observed that the field 

 mice preyed upon the young broods of 

 the bumblebees, and, therefore, the more 

 the field mice, the fewer the bumblebees 

 and the less the clover. When cats were 

 plenty and preyed upon the field mice it 

 follow-ed that the more the cats, the fewer 

 the mice, the more the bumblebees, and 

 the more the clover. Therefore, the crop 

 of clover depended upon the presence of 

 cats in the neighborhood. 



John" Merle Coulter. 



