PTERIDOPHYTA. 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 
Fia. 110.—Sexual organs of Horsetail. A, sections of two antherids: an’, 
young, and an, mature, with escaping sperm-cells. B, section of an archegone, 
showing the germ-cell below. Highly magnified. 
bears upon its under surface five to ten spore-cases (Fig. 
109, B). The spores are spherical, and at maturity the 
outer wall splits spirally into four narrow filaments (eaters) 
which unroll when dry, and roll up around the spore again 
when moistened. Their office seems to be to aid in setting 
the spores free.from the spore-cases. 
414, The spores germinate soon after falling upon water 
