MUCILAGE-HAIRS 



209 



surface and thus attaching the tendril very firmly to its support. 

 Many parasites fasten themselves in a similar manner to the surface 

 of the host, before producing their actual haustoria. 



The fixation of many seeds and fruits in the soil is effected by 

 means of special mucilaginous layers : these are also of some importance 

 in connection with water- 

 storage, a point which 

 will be more fully dis- 

 cussed in a subsequent 

 chapter (Chap. VIII. ). A 

 comparatively specialised 

 type of structure is ex- 

 emplified by the seed-coat 

 of Ruellia, where peculiar 

 mucilage-hairs are pre- 

 sent. In B. strepens the 

 walls of each hair con- 

 sist of a number of lay- 

 ers which swell greatly 

 in contact with water, 

 and of a thin cutinised 

 stratum which is provided 

 with numerous internal 

 annular thickenings. 

 When swelling takes 

 place, the hairs, which 

 in the dry state are 

 closely appressed to the 

 surface of the testa, 

 gradually erect them- 

 selves and at the same 

 time twist in various 

 directions : in so doing 

 they elongate very con- 

 siderably, while the in- 

 ternal layers of the wall swell so as to obliterate the cell-cavity almost 

 entirely. The cutinised layer is consequently torn across into a number 

 of strips, which, on account of their annular thickenings, act as so many 

 hoops binding the mucilaginous layers together. The most remarkable 

 mucilage-hairs occur in the seed-coats of certain Lythkaceae ; they 

 were first observed by Kiarksou, and have been described in greater 

 detail by Kohne, Klebs and Correns. 114 In this instance the so- 

 called hairs are not trichomes in a morphological sense at all. In 



o 



Fig. 80. 



L.S. through one of the barbed appendages of the fruit of 

 Cynoglosswu cheirifolium. 



