ON THE STUDY OF ADAPTATION IN PLANTS. 189 



which caused the production of cork ; as the result of the 

 effects of stresses and strains the mechanical cells were 

 developed, the corolla is supposed to have been evolved 

 from the stamens, as the direct result of the stimulus due to 

 the continual irritation and damage caused by insects in their 

 search after pollen or honey. Disregarding this last hypo- 

 thesis, which can only be designated as a fantastic picture, 

 we may inquire whether the marked distinction which Nageli 

 drew between transitory and permanent influences can really 

 be proved to exist. The difference might lie in the different 

 possibilities of response evinced by different plants, just as 

 a soft rod of iron which is magnetised soon after loses the 

 magnetism, whereas a steel rod retains it. 1 Doubtless the 

 theory of direct influence, which in a certain sense goes 

 back to Lamarck, has much that is very attractive. It 

 would also explain far more easily why organs, which 

 have become useless, so frequently become reduced, and 

 I should wish — in opposing Nageli's views — to point espe- 

 cially to the study of the transitory influences, from which 

 we should derive further valuable hints. 



We must not, however, forget that such adaptations 

 are only relative and conditioned by the organisation of 

 the plants in question. In the Darwinian theory ol 

 adaptation, organisation and adaptation are coincident, as 

 the former arises from the gradual accumulation of uselul 

 alterations. But even on this explanation a series ol 

 organic conditions remains incomprehensible, especially the 

 division of labour which has really nothing to do with 

 adaptation. In a genus of Hepaticee, Sympkyogyna, there 

 are species, the vegetation body of which lorms a Thallus. 

 and others in which it is present as a leafy shoot. 



It is inconceivable why the leaf-formation should be more 

 useful than the Thallus-formation. And the same is true 

 in the case of Fucus and Sargassum. According to the 



1 The aerial roots of some orehids become flattened and change 

 their structure on the side exposed to the light, and this does not occur 

 on the shady side. This dorsiventrality in some formations (Sarcanthus, 

 Phalxnopsis) is directly due to the operation of light. In others 

 {Aeranthus funalis) it is hereditary, and independent of light. 



