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 amabilis, and are also 
well known in several species of Galium. In Galium 
verum and G. Atoarine I have collected them in this 
A. 
neighborhood. Equisetum is also a well-known example, 
which deserves special mention as belonging to the vas- 
cular cryptograms as well as on account of its peculiar 
leaf-whorls. Our figure 126 is photographed from a 
stern 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 spiral torsions 
in species from which otherwise they can be obtained 
only very rarely. As instances of such species I may 
