230 



PLANT LIFE. 



irregularly thickened (see fig. 401). The strains caused by 

 the unequal absorption and loss of water burst the sporangium 



at some definite j)oint. This 

 line of dehiscence is often 

 between a pair of large sad- 

 dle-shaped cells (fig. 401). 



324. Sporophylls. — In 

 many of the ferns the leaves 

 which produce sporangia are 

 not different from the foliage 



Fig, 232. 



Fig. 233. 



Fig 232. — Diagram nf a longitudinal and transverse section of the very young capsule 

 of a true mobS ilh yma). The transverse section is taken along the line AJ<. <^ the 

 mother cells of the spores ; f, the columella ; h. intercellular space. The constriction 

 at the top marks the limit of the lid. The part below the sporangium is the neck, with 

 nutriti\'e tissues, — ( )riginal. 



Fig, 233, — A leaflet of a fern [As/'iditn") seen from the back, Ei,ght sori arc shcAvn, 

 each covered by its own indusiurn, /, Magnihed 2 diam, — ^^fter .Sachs, 



leaves. In others, certain leaxes are so siiccialized for 

 bearing the sporangia that they lose their nutriti\e function 

 in part or entirely. To such specialized leaves the name 

 spuruphvll is applied. 



325. Horsetails. — In the horsetails the sporangia lia\e the 

 form of sacs, varying in number from six to twehe. They 

 arise upon the lower face of a shiel(l-sha]ied sporojihyll (figs. 

 235, 236). These sporophylls are aggregated in a close 

 cluster at the upper end of the axis, constituting \'\-hat 



