HORSETAILS 



89 



a great number of spirally arranged sporophylls. Each 

 sporophyll is differentiated into a stalk and a shield-like outer 

 part; from the under surface develop up to ten elongated 



FIG. 49. Equisetum arvense. Five figures showing the development of the 

 ,gametophyte from the asexual spore. 



sporangia. When the spores are mature the sporangia open 

 and the spores, which have four hygroscopic bands terminat- 

 ing in a broad spatulate apex, will when the air is dry be 

 carried by the air currents far from the parent plant. 



