1920] 



WRIGH T—PI T-CLOSLXG ME 1 / BRA XE 



243 



stained red primary wall. In the pits, the unlignified membrane, 



form of a long spindle-shaped torus 



metaxyl 



Fig. 8 



lying across the space where the walls of adjacent tracheids have 



A slight thickening was found 



been 



torn apart in sectioning. 



also in the first-formed elements of the metaxylem. The tracheids 





Fig. 15 



Fig. 16 



Fig. 17 



Fig. 18 



Figs. 15-18. — Fig. 15, Botrychium obliquum: radial section of the rhizome show- 

 ing pitting and torus; X1200; fig. 16, Ophioglossum vitlgatiim: rhizome showing pit 

 membrane; X900; fig. 17, Ophioglossutn vulgatum: root in cortex showing membrane; 

 X900; fig. 18, Helminthostachys zeylanica: longitudinal section of rhizome showing 

 torus; X900. 



longitudinal 



thinning 



membrane with 

 edges of the pit. 



In Botrychium two types of torus occur. The most common 

 type is that seen in figs. 9 and 15, a long, slender, and rather vari- 

 able spindle. This is found in the mature wood of the stem, the 

 root, and the leaf trace in the cortex. 



mem 



brane 



from 



section in fig. 1 1 . The arrow in a tracheid to the right of the 

 center points to a fairlv thick membrane of the uniform type. 



