vni EFFECTS OF LIGHT AND GRA VITY 401 



hypothetical. He speaks of the explanation of the gradual 

 increase in height of plants on the earth, and says : " If we 

 start from the conception that the geotropic and heliotropic 

 organs were first produced under the influence of gravity and 

 light, it follows according to the views now current upon the 

 evolution of organisms, that wherever other conditions were 

 also favourable, more and more lofty forms must have been 

 produced, till at last the existing giants of the vegetable king- 

 dom were developed." And in a previous passage : " After 

 I had demonstrated the influence of gravity and light on the 

 development of roots and sprouts, the idea naturally offered 

 itself that the fundamental contrast between the two was to 

 be regarded as a gradually accumulated effect of these two 

 forces, especially of gravity. In fact, it would appear very 

 strange if these forces, notwithstanding their constant in- 

 fluence, had produced no hereditary properties. When we 

 reflect that the pace to which a mare is trained is inherited 

 by the filly, we are logically compelled to look for the heredi- 

 tary result of those forces in the organisms on which they 

 have acted in the same way for inconceivable periods of time. 

 If such a result were not present it would be in the highest 

 degree surprising." l 



Vochting thus meets the arguments by which Sachs 

 opposes his view, that the results of his experiments on the 

 recrescence of plants are to be regarded as phenomena of 

 heredity. Sachs looks upon these phenomena as the result 

 of the influence of gravity on the young growing organs. 

 The opposing action of light and gravity does not, he says, 

 depend on heredity, but the contrast represents only a " pre- 

 disposition," which is implanted in the organs of every 

 individual by light and gravity during its development. 2 



1 Cf. H. Vochting, Ueber Spitze und Basis an den Pflanzenorganen, 

 Botan. Zeitung, pp. 596-97. 



2 J. Sachs, Stoff und Form der Pflanzenorgane, Arbeiten des bot. Inst. zu 

 Wiirzburg, Bd. ii. p. 469, et seq. 



2 D 



