PTERIDOPHYTES 



301 



Oametophytes and macrosporangia bear macrospores which pro- 

 duce female Gcimetophytes. 



The Equisetales (Fig. 150) or horsetails or scouring inishes 

 is a small group of fern-like plants which grow from imder- 

 ground stems or rhizomes. One of the most common species is 

 Equisetum arveiiae. These underground s.t©ms bear tuber-like 

 storage organs and the aerial stems are produced annually. 

 There are two types of aerial stems; one is branched, giving a 



Fig. 150. — Equisetum arvense. (a) Underground stem and leafy shoot; (e) sporophyll; (& 

 and c) sporangia; (d) spores showing elaters; (/) male prothallus; (g) female prothallus. 



bvishy effect, grows throughout the summer, is green and serves 

 for foliage. The other bears rudimentary, collar-like structures 

 (or fused leaves) at the nodes and a cone-like structure (or stro- 

 bilus) at the top. These cones are made up of specialized leaves 

 (sporophylls) bearing the spores. Each spore has four elaters, 

 all attached at one point, which respond to moisture, winding and 

 unwinding in a manner which helps in their distribution. The 

 Gametophytes are of two kinds (dioecious), male and female, and 

 the archegonia and antheridia are practically the same as those 

 found in the ferns. 



