210 



MECHANICAL SYSTEM 



Cuphea viscosissima each epidermal cell of the dry seed-coat contains an 

 irregularly coiled thread-like protuberance, projecting inwards from its 

 outer wall and almost filling its cavity (Fig. 81). This coiled filament 

 is covered with grooves arranged in very gently ascending spiral series. 

 On the access of water, a circular patch of the outer wall immediately 

 overlying the insertion of the filament breaks away on one side like a 

 lid, and the filament begins to turn inside out. In this way a "hair" 

 is produced, the wall of which consists of the everted outer mem- 

 brane of the filament, while the swollen contents of the latter now form 

 a coating of mucilage on the outside of the hair. As the filament 



Pig. 81. 



Mncilage-hairs of the seed of Cuphea petiolata. a, T.S. through the testa ; s, epidermis ; 

 p, parenchyma ; m, stereides ; b, two epidermal cells more highly magnified ; c, part 

 of an everted hair. After Kiel is. 



turns inside out, its spiral folds straighten themselves more or less 

 completely. Correns has shown that the energy required for the 

 eversion of the filament is derived from the swelling of a substance 

 contained in the cell-cavity ; the same agency may even produce a 

 certain amount of " turgescence " in the completely everted hair. 



A totally different mechanical function is performed by the so-called 

 eel-trap hairs (Reusenliaare), which are developed in connection with 

 certain ecological relations between plants and crawling insects or 

 other minute animals. We have already had occasion, in discussing 

 trichomes in general, to mention the fact that stiff' hairs are often 

 directed obliquely downwards, especially on stems and petioles, so as to 

 act as obstacles to insects which may attempt to crawl upwards. In 

 such cases the aim in view is of course the repulse of "unbidden guests" ; 

 in the insectivorous genus Sarraeenia, on the other hand, the eel-trap 

 hairs serve to prevent the escape of captured animals. The pitchers of 

 Sarraeenia purpurea are furnished with two different kinds of these 



