Common Horse-Tail, etc. — continued. 



Genus. — Equisetum — the only genus. 



Species. — Arvense — Ixaf-sheaths of fertile stem, loose and distant. 



Maximum — Leaf-sheaths of fertile stem, large, loose, and close together. 



Difference from Ferns. — In Ferns, the fertile leaves bearing the sporangia are not usually confined to any particular part, and they act 

 both as ordinary green leaves and as spore-carriers. In Equisetum, different stems are produced at different seasons 

 of the year lor these two purposes. The Barren stems are green, and their sole work is to store up nutriment 

 in the underground stem. The Fertile stems do nothing towards their own support, but use up the accumulated 

 nourishment, in order to produce the spores. 



The majority of Ferns, too, produce Antheridia and Archegonia on the same prothallus; whereas in Equisetum the 

 two are kept separate, the male prothallus being smaller than the female. 



Pilularia— Fructification. 



Pillwort occurs by the margins of lakes or ponds, or in badly drained places. It has a wiry, creeping rhizome, which gives off 

 roots on the under surface, narrow stiff leaves on the upper surface, and terminates in a growing bud. Tittle pill-like bodies occur 

 towards the autumn, at the base of several of the leaves, either at or beneath the surface, and these are the Fruits. These fruits con- 

 tain spores of two kinds— Micro-spores or Male spores, and Macro-spores or Female spores. No male prothallus is formed, and only a 

 small female prothallus with a single Archegonium. 



Fig". 13. Rhizome, slender and creeping, ending in a terminal bud. 

 Roots, from under surface. / 



Leaves, in two rows, youngest always nearest the growing point. 

 Fruits, at the base of the leaves. 



Fig. 14. Embed Fruit in paraffin and make sections. 



Fruit consisting of four segments, supposed to be modified leaves joined edge to edge, the midrib represented 

 by central fibro-vascular bundle in each. 



Each segment with three fibro-vascular bundles, the middle one forming the core of a projecting cushion on 

 which the spore-cases are produced. 



Sporangia borne on the inner surface of modified leaves arranged in a whorl, containing Microspores and Macro- 

 spores. 



Fig. 15. Micr6spores examined under low power — average size about v $ v inch in diameter. 



The Microspore forms no male prothallus, but its contents break up directly into Antherozoids. The tri-radiate 

 markings show the lines along which the spore splits to allow the escape of the Antherozoids. 



Fig. 16. Macrospore examined under high power. 



Contents. — Cavity filled with nutritious substances, such as starch and oil globules. 

 Investments. — Four coats of varying quality,, formed in succession from within outwards. 



Inner coat, compact, the first formed coat. 



Hyaline coat, forming papilla at apex. 



Third coat, with radiating structure. 



Outer gelatinous coat, with concentric and radiating structure. This outer coat swells up with water. 



