The Significance of the Atavists. 555 



character, but that two antagonistic factors are at work, 

 the one excluding the other, ahhough never completely. 

 Even the stems with the most pronounced torsions pro- 

 duce branches, most of which revert to the decussate 

 arrangement of leaves. It never occurs that this char- 

 acter is completely excluded from the whole plant. Con- 

 versely, as we have already seen, atavistic individuals 

 with perfectly erect main stems and with a decussate or 

 ternary arrangement of the leaves frequently exhibit 

 torsions in their lateral branches. In 1887 I cut half the 

 atavists of my culture of Dipsacus syhestris torsiis close 

 down to the ground; they shot out from the base of the 

 stem. In this way I obtained about 2000 branches of the 

 second and third order. Amongst them 235 had a slight 

 but quite definite torsion and 26 had a small many-leaved 

 spiral. In the third generation I repeated the experiment 

 with the same result; and moreover observed torsions 

 on the lateral branches of some atavists which had been 

 allowed to remain on the l)e(ls until they were just about 

 to flower. 



Other abnormalities in the arrangement of leaves also 

 betray the real nature of the atavists. First, there are the 

 individuals with ternary whorls. Sucli whorls do not 

 occur in the early stages of the plant, and tricotylous 

 seedlings are even very rare. At first the arrangement 

 of the leaves is always decussate, and it is not until late 

 summer or autumn, at the time when other specimens 

 begin to produce their leaves in a spiral, that the decussate 

 arrangement gives place to a ternary one. But when 

 this has once appeared it usually remains on the stem 

 up to the terminal flowerhead. Such plants look quite 

 normal, ai^l especially their leaves do not ])ro(luce those 

 forkings of the mid-rib which are so common in the 



