IV. HERITABLE SPIRAL TORSIONS. 
(Plate VI.) 
18. THE SPIRAL DISPOSITION OF THE LEAVES. 
In the case of spiral torsion the difference between 
normal and abnormal individuals is far more striking 
than in that of fasciations. Valeriana officinalis is one of 
the best known and the most frequently figured instances 
(Fig. 122). Here the whole stem, instead of growing 
to a height of more than a meter, can be reduced to about 
a decimeter, and becomes more or less funnel-shaped. 
Low down the leaves are disposed spirally, but higher up, 
the spiral gradually becomes steeper, until, in the ex- 
panded upper part of the funnel all the leaves are directed 
to one side like a fan. The terminal inflorescence sur- 
passes the highest lateral flowering branches very little 
or not at all. 
By no means every stem of the spirally twisted plant 
manifests the anomaly. On the contrary, very few of 
them do as a rule. Since 1889, I have had a specimen 
which has gradually increased by runners and now covers 
an area of several square meters in the botanical garden 
of Amsterdam. It produces spiral torsions every year, 
but they are rare, and, as a rule, there are not more than 
two or three among several hundreds of normal stems. 
The same rarity is seen in the inheritance of the 
anomaly, both in Valeriana and other species ; as a rule, 
