TYPES OF CRYPTOGAMS; PTERIDOPHYTES 293 



above ground insert here any evident points of comparison. Do you 

 find any special forms of stern development suited to a special pur- 

 pose ? Are there any organs in the nature of leaves ? 



FIG. 213. A Scouring-Rush (Equisetum sylvatlcum). At the right is a 

 colorless fertile stem, in the middle a green sterile one, and at the 

 left a green fertile one. 



