642 Mutations 



partly because the division of labor is indicative 

 of a higher degree of evolution. But sometunes 

 these dimorphic species are seen to revert to the 

 primary condition, developing a fertile cone at 

 the summit of the green summer-stem. I have 

 had the opportunity of collecting an instance of 

 this anomaly on the tall Equisetum telmateja 

 in Switzerland, and other cases are on record in 

 teratological literature. It is an obvious ex- 

 ample of systematic atavism, occurring sud- 

 denly and with the full development of all the 

 qualities needed for the normal production of 

 sporangia and spores. All of these must be 

 concealed in a latent condition within the young 

 tissues of the green stems. 



More than once I have had occasion to deal 

 with the phenomenon of torsions, as exhibited 

 by the teasels and some other plants. This 

 anomaly has been shown to be analogous to the 

 cases described as double adaptations. The 

 capacity of evolving antagonistic characters is 

 prominent in both. The antagonists are as- 

 sumed to lie quietly together while inactive. 

 But as soon as evolution calls them into activity 

 they become mutually exclusive, because only 

 one of them can come to full display in the same 

 organ. External influences decide which of the 

 two becomes dominant and which remains dor- 

 mant. This decision must take place separately 



