IV. HERITABLE SPIRAL TORSIONS. 



(Plate VI.) 



§ i8. THE SPIRAL DISPOSITION OF THE LEAVES. 



In tlie 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). Llere 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 

 wliich has graduallv increased by runn.ers and now covers 

 an area of several square meters in the botanical garden 

 of Amsterdam. It produces spiral torsions every year, 

 Imt 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 sjiecies ; as a rule. 



