TYPES OF CRYPTOGAMS; PTERIDOPHYTES 293 
above ground insert here any evident points of comparison. Do you 
find any special forms of stem development suited to a special pur- 
pose? Are there any organs in the nature of leaves? 
Fie. 213.— A Scouring-Rush (Equisetum sylvaticum). At the right is a 
colorless fertile stem, in the middle a green sterile one, and at the 
left a green fertile one. 
