266 



MOSSES AND FERNS 



CHAP. 



sieve-tubes consist of a thin parietal layer of protoplasm in 

 which numerous nuclei are imbedded. Little glistening glob- 

 ules are also found, especially close to the openings of the pores 

 of the sieve-plates. 



The lamina of the sterile segment of the leaf is composed 

 of a spongy green mesophyll, more compact on the upper sur- 

 face. The epidermal cells show the wavy outlines characteristic 

 of the broad leaves of other Ferns, and develop stomata only 

 upon the lower side of the leaf. 



Fig. 146. — Botrychium Virginianum. A, Longitudinal; B, transverse sections of the 



root apex, X200; pi, plerome. 



The Root 



The roots arise singly at the bases of the leaves, and in 

 older plants branch monopodially. Like those of Ophioglossum 

 they have no root-hairs, but the smooth surface of the younger 

 roots becomes often strongly wrinkled in the older ones. Sec- 

 tions either transverse or longitudinal, through the root tip, 

 when compared with those of Ophioglossum, show a very much 

 greater regularity in the disposition of the cells. This is less 

 marked in B. ternatum, and probably an examination of such 

 forms as B. simplex will show an approximation to the condi- 

 tion found in Ophioglossum, although Holle's figure of B. luna^ 



