Rare Spiral Torsions. 537 



sibly be raised by selection. At present, however, the 

 annual habit and the torsion are mutually exclusive, the 

 anomaly being represented on the stems of such plants 

 either not at all or as faint indications only. 



§ 19. RARE SPIRAL TORSIONS. 



From time to time spiral torsions are also found on 

 wild and cultivated plants under conditions which make 

 it impossible to make any other observations on the in- 

 heritance of the anomaly than that they occur relatively 

 frequently on the several branches of the same plant or 

 in more or less numerous examples in the same locality ; 

 or recur during the course of several years. They may 

 be found in dozens in Weigelia amahilis, and are also 

 well known in several species of Galium. In Galiinii 

 venim and G. At>arine I have collected them in this 

 neighborhood. Eqiiisctiim is also a well-known example, 

 which deserves special mention as belonging to the vas- 

 cular cryptograms as well as on account of its j^eculiar 

 leaf-whorls. Our figure 126 is photographed from a 

 stem which Dr. Th. Weevers found near Nymegen in 

 the summer of 1900. Here it grew among several other 

 instances of torsion in the same species. Casuarina also 

 sometimes forms such anomalies on its branches ; for 

 instance, several occurred in 1897 in the botanical garden 

 of Amsterdam (Fig. 127 a). 



In the first chapter of this part we have seen how, 

 as a result of the correlation between various abnormal 

 types of leaf arrangement, the selection of tricotylous 

 seedlings often leads to the discovery of s])iral torsions 

 in species from wdiich otherwise they can be ol^tained 

 only very rarely. As instances of such species I may 



