TRACHEARY TISSUE. 



85 



duct, but pass into separate circles on the other, forming an 

 annular duct. This kind of duct is found associated with the 

 spirals in the Geranium. The two are closely related. The 

 spirals and rings may be close together or wide apart and the 

 rings may be at various inclinations to the length of the duct. 

 The spiral ducts are smaller in diameter than the reticulate 

 (Fig. 51). 



SCALARIFORM DUCTS IN FERNS. 



These ducts have their thickenings arranged like the rounds 

 of a ladder, hence the name scalariform. They occur in many 

 plants, but they are seen to best advantage in the ferns, where 

 they are beautifully developed and almost to the exclusion of all 

 other woody tissue in the bundles. 



Make thin longitudinal radial sections of the rhizome of the 

 official Male Fern or of the Eagle Fern (Pteris aquilina) , stain in 

 methyl-green or phloroglucin and hydrochloric acid and mount 

 in water. The ducts will be stained green or red; they are 

 mostly prismatic or flat-sided where they press upon one an- 

 other, and at the edges where the sides meet there is a thickened 

 ridge. Crossing the flat faces are numerous parallel thick 

 ridges separated by very thin places looking like slits. The 

 faces have the appearance of a ladder. The ducts are oblique 

 or taper-pointed, large in diameter and the ends splice over one 

 another (Fig. 51). 



Isolate the ducts by maceration in Schulze's solution as in the 

 previous cases. 



Fia. 51. Various tracheary ducts. 1 and 2, spiral ; 3, combined annular and spiral ; 

 4, scalariform ; 5, reticulated. 



TRACHEARY TISSUE OF GYMNOSPERMS. 



TRACHEIDS WITH BORDERED PITS. These peculiar cells, 

 although occasionally found in other plants, are characteristic 

 of gymnosperms. In these plants ducts and wood cells are rare, 

 being replaced by tracheids, which constitute nearly the whole 



