v.] NEW ADAPTATIONS 41 



taneously at first by congenital variation, and 

 then have been " selected " etc. ? Or was it the 

 actual contact which excited the protoplasm, so 

 to say, to invent and then make them ; and so 

 they became hereditaiy in course of generations ? 



Analogy will throw some light upon this. 

 Members of the cucumber family, which climb 

 like the wild bryony, have long tendrils which 

 'twine round the supporting object ; but a certain 

 plant of a Trichosanthes happening to have its 

 tendrils touching the wall of the glass frame in 

 which it grew, instantly developed a number of 

 minute pads which adhered to the wall (fig. 10), 

 though such a structure is not known to exist 

 in the cucumber family at all. Here, then, as 

 far as has been observed, the pads suddenly 

 arose de novo, merely by the accidental irritation 

 of the tips of the thread-like tendrils. 



A common sea - weed Plocamium coccineum 

 (fig. 11), is known to make similar pads if a 

 tip happen to press against another sea- weed ; 

 though it has no need to climb. But there 

 are many cases of a mere mechanical force 

 producing through response hereditary structures. 



It is well known that the stems of lianes are 

 very anomalous in their internal anatomy, the 

 prevailing features are a degradation of the 

 supportive or woody tissues, and much increase 

 of the cellular structures, as the medullary rays 

 and cortex. This is in accordance with habit, for 



F 



