190 EFFECT OF KILLING PKIMAKY RADICLE. Chap. Ul 



the primary radicle or of tlie leading shoot. The 

 following considerations give us, as we believe, the 

 clue. Firstly, any cause which disturbs the con- 

 stitution* is apt to induce reversion; such* as the 

 crossing of two distinct races, or a change of con- 

 ditions, as when domestic animals become feral. 

 But the case which most concerns us, is the frequent 

 appearance of peloric flowers on the summit of a stem, 

 or in the centre of the inflorescence, — parts which, it is 

 believed, receive the most sap ; for when an irregular 

 flower becomes perfectly regular or peloric, this may 

 be attributed, at least partly, to reversion to a primi- 

 tive and normal type. Even the position of a seed at 

 the end of the capsule sometimes gives to the seedling 

 developed from it a tendency to revert. Secondly, 

 reversions often occur by means of buds, independently 

 of reproduction by seed ; so that a bud may revert to 

 the character of a former state many bud-generations 

 ago. In the case of animals, reversions may occur in 

 the individual with advancing age. Thirdly and 

 lastly, radicles when they first protrude from the seed 

 are always geotropic, and plumules or shoots almost 

 always apogeotropic. If then any cause, such as an 

 increased flow of sap or the presence of mycelium, 

 disturbs the constitution of a lateral shoot or of a 

 secondary radicle, it is apt to revert to its primordial 

 state ; and it becomes either apogeotropic or geotropic, 

 as the case may be, and consequently grows either 

 vertically upwards or downwards. It is indeed pos- 



* The facta on which the fol- xiv. On peloric flowers, chap, 



lowing conclusions are founded xiii. p. B2; and see p. 337ontbeii 



are given in ' The Variation of position on the plant. With 



Animals and Plants under Domes- respect to seeds, p. 340. On re- 



ticatlon,' 2nd edit- 1875. Ou the version by means of buds, p. 438 



causes leading to leversiim see chap. xi. vol. i. 

 chap. xii. vol. ii. acd p. 59, chap. 



