FERTILIZATION AND CROSS-FERTILIZATION. 27 



In the Kalmia^ or mountain laurel, the anther is in a pocket and held 

 down so that the filament is bent, and when released the pollen 

 escapes through an opening at the top. The effect is similar to 

 that which might be produced by a boy fastening a case of shot on 

 the end of a whalebone rod, and then bending the rod and suddenly 

 releasing it. At first sight this arrangement might appear well 

 adapted to secure the fertilization of a flower b}' its own pollen, but 

 it is found that the pollen generally shoots clear by the stigma. 

 When, however, an insect ahghts on the flower and covers the 

 stigma, the under side of his body takes the pollen, where it is 

 ready to be imparted to the stigma of the next flower on which he 

 lights. That the pollen of this plant is not very potent in self- 

 fertilization was shown by Professor Beal, who covered up a plant 

 with gauze so that no insect could get to the blossoms, and in this 

 case no good seed set. The barbeny presents a well-known case of 

 sensitiveness in the filaments. The lecturer called attention in 

 passing to the curious fact, that by the application of chloroform the 

 stamens lose their sensitiveness ; the same is true also in the sensi- 

 tive plant. When an insect ahghts on the barberry, the stamens fly 

 up, the anthers open bj' trap-doors, and the pollen comes side fore- 

 most and falls on the insect instead of on the stigma. This was 

 noticed by Sprengel, who also observed that the barberry was visited 

 generally by sluggish insects. In the common iris, the pollen is 

 below the stigma, and the insect in its search for nectar carries oS 

 the pollen from the anther to another flower. 



But the most remarkable contrivances for ensuring cross-fertili- 

 zation are found among Orchids. These are so numerous and 

 so curious that Darwin has written a book on the subject. A 

 species of Habenaria has a broad hp with an open space, on each 

 side of which is a case containing a packet of pollen. The nectar 

 is at the bottom of a long tube or spur, down which the insect must 

 reach to obtain it, though some insects have become so lazy as to 

 shirk this duty and open the base of the tube, and the same opera- 

 tion has been noticed in the columbine. In reaching down the tube 

 the head of the insect comes in contact with two sticky discs, which 

 fasten themselves to his head, and he flies with them to another 

 flower. When these discs first attach themselves to the head of 

 the insect, having been in a moist place the pollen-masses are damp 

 and project from his head, but soon dry and curve downwards and 

 forwards. The insect flies to another flower, and in seeking to 



