86 



CERATOPHYLLUM 



[CH. 



r..-- 



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. (I8Q4 1 ).] 



The forked leaves characteristic of the mature plant (/ in 

 Fig. 54 A) 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 1 : "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 2 . 



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. 56). 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 3 . There is complete absence of 

 lignification. 



The water content of the plant is very high, representing 

 88 per cent, of the total weight 4 , 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 5 . They seem to differ from the common mucilage hairs 



i Schleiden, M. J. (1837). 2 Wylie, R. B. (1912). 



3 Sanio, C. (1865). 4 Schleiden, M. J. (1837). 



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



