FIG. 284. A horsetail (Equisetum arvense) 



A, fertile stems, bearing cones rising from the creeping rootstock : t, tuberous 

 bodies; v, young vegetative stern below ground and ready to grow into the 

 mature structure shown in B. 13, vegetative stem as it appears perhaps three 

 weeks after the fertile stems have shed their spores and died. C, a group of 

 spores with their elaters expanded. Z), a spore with the elaters coiled around 

 it. E, two views of the spore leaves (sporophylls), showing the group of spo- 

 rangia. F, portion of a section of the stem: a, air spaces; c, chlorophyll-bear- 

 ing tissues ; r, rigid outer tissues ; /, fibro-vascular bundle around small air 

 space. A, B, C, D, after Schenck 



326 



