Chap. X. SECRETION OF NECTAR. 403 



There is no great difficulty in understanding how an 

 anemophilous plant might have been rendered entoroo- 

 philous. Pollen is a nutritious substance, and would 

 soon have been discovered and devoured by insects, 

 and if any adhered to their bodies it would have been 

 carried from the anthers to the stigma of the same 

 flower, or from one flower to another. One of the chief 

 characteristics of the pollen of anemophilous plants 

 is its incoherence ; but pollen in this state can adhere 

 to the hairy bodies of insects, as we see with some 

 Leguminosae, Ericaceae, and Melastomacese. We have, 

 however, better evidence of the possibility of a tran- 

 sition of the above kind in certain plants being now 

 fertilised partly by the wind and partly by insects. 

 The common rhubarb (Rheum rhaponticum) is so far 

 in an intermediate condition, that I have seen many 

 Diptera sucking the flowers, with much pollen adhering 

 to their bodies; and yet the pollen is so incoherent, 

 that clouds of it are emitted if the plant be gently 

 shaken on a sunny day, some of which could hardly 

 fail to fall on the large stigmas of the neighbouring 

 flowers. According to Delpino and H. Miiller,* some 

 species of Plantago are in a similar intermediate 

 condition. 



Although it is probable that pollen was aboriginally 

 the sole attraction to insects, and although many 

 plants now exist whose flowers are frequented exclu- 

 sively by pollen-devouring insects, yet the great 

 majority secrete nectar as the chief attraction. Many 

 years ago I suggested that primarily the saccharine 

 matter in nectar was excreted f as a waste product of 

 chemical changes in the sap ; and that when the ex- 



* DieBefruchtuug,'&c. p. 31'2. excretion, as stated by Martinet 

 t Nectar was regarded by in' Annal. desSc. Nat.' 1872, torn. 

 De Candolle and Dimal as an xiv. p. 211. 



2 d 2 



