xix] FIXATION OF SEEDLINGS 245 



means of an absciss layer. There are exceptions, however, to the 

 general rule that the radicle of water plants is poorly developed : 

 in Lobelia Dortmanna, for example, it attains fair dimensions 1 . 



In the case of those water plants which grow rooted in the 

 soil, the poor development of the radicle is often compensated, 

 at an early seedling stage, by the production of a garland of very 

 long root-hairs, which grow out from the 'collet,' or junction 

 of hypocotyl and root, e.g. Hippuris 2 , Elatine hexandrcP (Fig. 

 158) and many Helobieae 3 ' 4 , such as Zannichellia (Fig. 159 C, 

 p. 246). This type of seedling is, however, by no means confined 

 to hydrophytes, but is also found in a number of land plants. 



The weight of the large seed tfNelumbo*, and of the achene 

 wall in the case of the small seedling of Zannichellia 5 (Fig. 1 59), 

 are sufficient to keep the seedling steady at the bottom of the 

 water until the epicotyl and first leaves are produced. Other 



FIG. 158. Elatine hcxandra, D.C. Germination of seed ; s, seed- ^L ^\ 



coat; h, wreath of hairs growing from collet and surrounding V^ JTN 

 the primary root which forms a minute conical structure. ) I i 



[Klebs, G. (1884).] tffW^ 



seedlings are anchored for some time by the fruit wall and associ- 

 ated structures : the grappling apparatus viCymodocea antarctica, 

 for instance, has been already described 6 . In Trapa natans 1 

 (Fig. 1 60, p. 247) the fixation of the seedling is accomplished 

 in an unusual way, for here the heavy nut sinks to the bottom 

 of the water, where it is held by hooks derived from the calyx. 

 Two structures of very unequal size (Co 1 and Co 2 ) are generally 

 interpreted as the two cotyledons, though possibly this view 

 is open to revision. The hypocotyl, including even its extreme 

 apex, which presumably is of root nature, is negatively geo- 

 tropic. The first lateral roots, borne by the hypotocyl, curve 

 downwards and anchor the plant in the soil, while many of the 



1 Buchenau, F. (1866). 2 Irmisch, T. 



3 Klebs, G. (1884). * Warming, E. (1883!). 



5 Hochreutiner, G. (1896). See p. 127. 

 7 Goebel,K. (1891-1893). 



