PLANT TISSUES 137 
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Fic. 75.—Types of tracheae and tracheids. A, annulo-spiral trachea; B, spiral 
trachea; C, tracheid with several rows of bordered pores; H, pitted vessel; £, 
portion of a coniferous tracheid with a single row of bordered pits; D, tangential- 
longitudinal section of a bordered pit and portion of adjacent wall shown in £, 
enlarged; p, pore or orifice pit; 4, eeteenns border; cm, limiting membrane which 
t); 
bears at its center a thickened pod or torus ¢, cavity of pit; F, reticulate trachea in 
longitudinal section; G, longitudinal section of spiral trachea. 
