142 EXPERIMENTAL EVOLUTION LECT. 



On the other hand, turning to plants, similar facts 

 of physiological or chemical variation are noticeable. 

 The same plant is more or less toxic, according to its 

 age or period of life, and to the various parts con- 

 sidered. While some plants are toxic in all their 

 parts, such as meadow saffron (Colchiciim autummale) 

 hellebore, squill (Scilla maritime), Pride of India {Melia 

 azcdaracli], others are dangerous only in their roots, 

 such as Atractylis gemmifera, or in their roots and 

 stem, such as the common dog violet ; or in their 

 aerial parts only, such as many Solanaceae ; or in 

 their bark and leaves only, as is the case with the 

 yew ; or in their flowers, as buckwheat (Polygonum 

 fagopyrum) ; or in their fruits only, as, for instance, 

 in the castor oil plant ; or even in one part only of 

 their fruits. Other plants are dangerous in all their 

 parts save one, the fruit for instance in sumach (R/ius 

 coriaria). 



Young leaves of the yew are much less toxic than 

 aged ones, which is the reverse of the case generally 

 observed. Clematis vitalba displays the same fact. 

 Ranunculus ficaria, while at first feebly toxic (through 

 its leaves), becomes afterwards more so, but after 

 flowering it loses much of its poisonousness, and the 

 same is the case with Caltha palustris. Aconitum 

 napellus is very toxic in warm climates, while in 

 the northern or cold regions it is harmless ; culti- 



