Latent Characters 239 



currence of negative ones. Indeed, if we put 

 aside the radiate and the color-varieties of 

 flowers and foliage, hardly any cases can be 

 cited. We have dealt with this question in a 

 former lecture, and may now limit ourselves to 

 the positive color- varieties. 



The latency of the faculty of producing the 

 red pigment in leaves must obviously be ac- 

 cepted for nearly the whole vegetable kingdom. 

 Oaks and elms, the beautiful climbing species 

 of Ampelopsis, many conifers, as for instance 

 Cryptomeria japonica, some brambles, the 

 Guelder-rose (Viburnum Opulus) and many 

 other trees and shrubs assume a more or less 

 bright red color in the fall. During summer 

 this tendency must have been dormant, and that 

 this is so, is shown by the young leaves of oaks 

 and others, which, when unfolding in the spring 

 show a similar but paler hue. Moreover, there 

 is a way of awakening the concealed powers at 

 any time. We have only to inflict small wounds 

 on the leaves, or to cut through the nerves or to 

 injure them by a slight bruising, and the leaves 

 frequently respond with an intense reddening of 

 the living tissues around and especially above 

 the wounds. Azolla caroliniana, a minute moss- 

 like floating plant allied to the ferns, responds 

 to light and cold with a reddish tinge, and to 

 shade or warmth with a pure green. The foli- 



