PTEBIDOPHTTA. 



197 



node, where they join with one another. They contain 

 tracheary, sieve, and fibrous tissues, arranged somewhat as 

 they are in the bundles of flowering plants. 



413. The spores of Horsetails are produced in cones at 

 the summit of the stems. The cones are composed of 

 crowded whorlS of shield-shaped leaves, each of which 



aw' 



Fia. 110. — Sexual organs of Horsetail. A, sections of two antherids; an', 

 youn^f and an, mature, with escaping sperm-cells. B, section of an archegone, 

 showmg the germ-cell below. Highly magnified. 



bears upon its under surface five to ten spore-cases (Fig. 

 109, S). The spores are spherical, and at maturity the 

 outer wall splits spirally into four narrow filaments (elaters) 

 which unroll when dry, and roll up around the spore again 

 when moistened. Their ofiice seems to be to aid in setting 

 the spores free from the spore-cases. 



414. The spores germinate soon after falling upon water 



