Fig. 55. Ceratophyllum de- 

 mersum, L. Seedling one 

 week old. (Enlarged.) c= co- 

 tyledon; /= member of first 

 pair of leaves which decus- 

 sate with the cotyledons; 

 r= rudimentary radicle which 

 never elongates. [Guppy, 

 H. B. (1894^).] 



86 CERATOPHYLLUM [ch. 



The forked leaves characteristic of the mature plant (/ in 

 Fig. 54 y^y p. 85) are not formed im- 

 mediately; they are preceded by a juve- 

 nile type which is simple and linear. 

 It is not until the fourth node above 

 the cotyledonary node that every mem- 

 ber of the whorl attains the characteristic 

 form. Each of the slender axes of the 

 mature plant, with its whorls of forked 

 leaves {B in Fig. 57, p. 89), often 

 occupies a more or less vertical position 

 in the water and quite deserves the 

 description given many years ago by 

 a German writer^: "A Christmas tree 

 for tiny water nixies." The Hornwort 

 sometimes flourishes at a considerable 

 depth; in Iowa it has been recorded to grow with marked success 

 beneath nearly thirty feet of water^. 



The stem structure of Ceratophyllum may be taken to repre- 

 sent one of the ultimate terms in the reduction series met with 

 among Dicotyledonous water plants (Fig. 5 6). The fully- 

 developed internode has a central axial passage which has arisen 

 through the resorption of a small group of narrow-lumened 

 thin-walled procambial cells^. There is complete absence of 

 lignification. 



The water content of the plant is very high, representing 

 88 per cent, of the total weight*, but as the young parts are 

 cuticularised to a degree unusual in submerged plants, the 

 texture of the shoots is less fragile than one might expect, and 

 collapse does not occur so rapidly in a dry atmosphere as in the 

 case of many hydrophytes. The curious mucilage-containing 

 hairs borne by the leaves, stamens, etc., have been much dis- 

 cussed^. They seem to differ from the common mucilage hairs 



1 Schleiden, M. J. (1837). 2 Wylie, R. B. (19 12). 



3 Sanio, C. (1865). * Schleiden, M. J. (1837). 



5 Goppert, H. R. (1848), Borodin, J. (1870}, Strasburger, E. (1902). 



