410 SEXUAL RELATIONS OF PLANTS. Chap. X, 



that plants, after having been once rendered entomo- 

 philous, should ever again have become anemophilous ; 

 but this has occasionally though rarely occurred, for 

 instance, with the common Poterium sanguisorba, as may 

 be inferred from its belonging to the Bosaeeas. Such 

 cases are, however, intelligible, as almost all plants 

 require to be occasionally intercrossed ; and if any 

 entomophilous species ceased altogether to be visited 

 by insects, it would probably perish unless it were 

 rendered anemophilous, or acquired a full capacity for 

 self-fertilisation ; but in this latter case we may 

 suspect that it would be apt to suffer from the long- 

 continued want of cross-fertilisation. A plant would 

 be neglected by insects if nectar failed to be secreted, 

 unless indeed a large supply of attractive pollen was pre- 

 sent ; and from what we have seen of the excretion of 

 saccharine fluid from leaves and glands being largely 

 governed in several cases by climatic influences, and 

 from some few flowers which do not now secrete nec- 

 tar still retaining coloured guiding-marks, the failure 

 of the secretion cannot be considered as a very im- 

 probable event. The same result would follow to a 

 certainty, if winged insects ceased to exist in any 

 district, or became very rare. Now there is only 

 a single plant in the great order of the Cruciferae, 

 namely, Pringlea, which is anemophilous, and this 

 plant is an inhabitant of Kerguelen Land,* where 

 there are hardly any winged insects, owing probably, 

 as was suggested by me in the case of Madeira, 

 to the risk which they run of being blown out to sea 

 and destroyed. 



A remarkable fact with respect to anemophilous 

 plants is that they are often diclinous, that is, they are 



The Rev. A. E. Eaton in 'Proc. Royal Soc' vol. xxiii. 1875, p. 351. 



