III.] ORCHIDACE^. 321 



comes in contact with the under viscid surface of one or of 

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

 withdrawing the pencil, the poUinia 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 be carefully watched munediately after they are withdrawn 

 from the anther, they may be observed to become inclined 

 fonvards 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 polhnia which adhere to the pencil will 

 strike against the viscid stigmatic surface of the flower, and 

 at least a portion of the pollen-grains will adhere to it and 

 fertilise the ovules of the flower. The viscidity of the 

 stigma is sufficient to overcome 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-fertilised. 

 Almost invariably insect aid is required to transport the 

 pollen from flower to flower ; hence the importance of the 

 contrivances indicated above (to which Mr. Darwin has 

 recently directed attention), to insure the proper fulfilment 

 of the important function assigned to unconscious agents. 



It is extremely desirable that similar observations should 

 be made upon living Indian species. In De?id?'obium Mr. 

 Darwin finds that the pollinia become attached to insects 

 visiting the flower by a viscid fluid, which is exuded by the 

 minute rostellum immediately under the anther, when the 

 projecting lip of the anther is pushed up by the retreat of 

 the insect from the short nectary. 



The very large Orchid Family is widely spread over the 

 globe. Most of the species with large showy flowers are 

 confined to tropical countries, and grow, not upon the 



Y 



