144 THE STRUCTURE OF FLOWERS. 



nectariferous, this would bear out the above remarks, for it 

 would be as easily accessible as in the case of Caltha. 



The merely occasional puncture and lesion caused by an 

 insect whicli then flies away and does not keep up tbe irrita- 

 tion — unless it be renewed by other insects — would not of 

 itself be hereditary.* Thus, for example, Anemone nemorosa 

 appears to be honeyless, but supplies pollen to bees ; yet 

 Miiller noticed them frequently probing between the sepals 

 and stamens, apparently to obtain juices wheremth to 

 moisten the pollen. This process may have been the actual 

 origin of nectaries, the result of a wound 'constantly repeated 

 and kept up, being a flow of a sweet secretion, which has thus 

 attracted insects and induced them to repeat the process. 



Analogous Cases. — A somewhat analogous illustration is 

 that of galls, but in them the presence of the eg^, and sub- 

 sequently the grub, keeps up the irritation. These remark- 

 able structures do not form spontaneously as nectaries now 

 do, without a puncture ; still, even in this case, there may 

 be, for all we know, a predisposition to form them ; perhaps 

 seen in the readiness with which the Oak forms so many 

 kinds, and they may be now, perhaps, much larger than they 

 were when insects of any particular species first punctured 

 the ancestral oak upon which so many kinds have now been 

 evolved. t The apex of a shoot of Yew attacked by Cecidomyia 

 taxi is transformed into a fleshy ring curiously resembling 

 the honey-disk of many flowers. 



It is well known that in the human subject there may be 

 a predisposition for tumorous or cancerous growths which 

 is hereditary; and there would seem to be a very close 



* Injuries, especially to the nerves, may be hereditary in man ; see 

 "Nature, xxiv., p. 257. 



t M. E. Heckel thinks that the female "gall-flowers" of the Fig, 

 with an abortive ovary, in which the Cynips blastophaga lays its egg, is 

 now an hereditary form {Bull. Soc. Bot. de Fr., 1886, p. 41). 



