45 S Eimer on Growth and Inheritance 



form of roots and causes them to grow towards the centre of 

 the earth ? ' That it has acted and acts therein we do not 

 question ; but we deny that it can be termed the determin- 

 ating agency, and we deny it on the strength of Professor 

 Eimer's own words. He tells us ^ that ' Vochtiug hung up a 

 twig of willow in a position the reverse of the natural, in a 

 vessel where it was exposed to moisture and the other condi- 

 tions favourable to growth. This twig produced roots not 

 only at the lower end, where their development was favoured 

 by gravity, but also, and in superior numbers, at the upper 

 end/ 



In that plant of the Cactus tribe named Lepismium radi- 

 cans, roots will be produced on any part of its sprouts from 

 which light is excluded. Nevertheless, as a rule, roots are 

 thrown out from the underside of plants only, as we should 

 naturally anticipate. 



With respect to the re-formation of parts removed — extra- 

 ordinary instances of the process of repair — Professor Eimer 

 remarks : — ^ 



'The old explanation was that it was due to the "formative 

 tendency," and this was deemed sufficient. We may still use the 

 same term, provided that we get rid of the meaning which the earlier 

 school attached to it, namely, that of a spontaneous impulse more or 

 less independent of matter. If we guard against this, and employ the 

 term in the sense of the action of definitely directed forces contained 

 in the material of the organism, then there is nothing to be said 

 against it.' 



But the earlier school, to which we presume Professor 

 Eimer refers, did not regard such impulse as in any way 

 ' independent of matter,' but as absolutely dependent upon 

 matter for its manifestation. It held, as we hold, no more 

 than what Professor Eimer must, if he is logical, mean when 



1 P. 400. 2 p, 393. 



