xm] MILFOIL AND HORNWORT 179 



Ceratophyllum (Fig. 56, p. 87), as we have already shown, 

 may be regarded as representing the extremest stage in the 

 simplification characteristic of the stem-anatomy of Dicotyle- 

 donous water plants. There is a central duct, surrounded by 



FIG. 1 1 6. Myriophyllum spicatum, L. T. S. moderately old 

 [Vochting, H. (1872).] 



FIG. 117. Myriophyllum spicatum, L. T.S. stele of young axis showing the scat- 

 tered internal vessels and eight phloem groups near the periphery of the stele. 

 (X2I5.) [Vochting, H. (1872).] 



elements whose walls are somewhat thickened, but consist of 

 cellulose only 1 . These thick-walled cells are again surrounded 

 by a broad zone of phloem 2 . 



In connexion with the strong tendency shown by aquatic 

 1 Sanio, C. (1865). 2 Schenck, H. (1886). 



