230 ORCHIDACE^E. [CLASS 



expanded flower, which has not lost its pollen, just as an 

 insect would insert its proboscis when in search of nectar. 

 It will be found that the pencil does not fail to push 

 against the projecting rostellum, so that the pouch-like 

 membrane of the latter is pressed down, and the pencil 

 conies in contact with the under viscid surface of one or 

 of both of the little glands of the two pollen-masses. On 

 withdrawing the pencil, the pollinia are found adhering 

 firmly to it, for the viscid substance which bathes the 

 glands sets hard in a few seconds when exposed. If the 

 pollinia be carefully watched immediately after they are 



FIG. 174. Single pollen-mass of: FIG. 175. Seed of same. 



Spotted Orchis, with its cau- 

 dicle and gland. 



withdrawn from the anther, they may be observed to be- 

 come inclined forwards to such an extent, that if, after 

 the lapse of a minute or two, the pencil be thrust into the 

 nectary of a second flower, the pollinia which adhere to 

 the pencil will stride against the viscid stigmatic surface 

 of the flower, and at least a portion of the pollen- 

 grains will adhere to it and fertilize the ovules of the 

 flower. The viscidity of the stigma is sufficient to over- 

 come the strength of the delicate threads which bind the 

 grains of pollen together. 



From the peculiar relative arrangement of the pollen- 

 masses and stigma in Orchids, Mr. Darwin has shown 

 that the flowers can be but very exceptionally self-fertilized. 



