THE FERN ALLIES. 33 



of teeth. These teeth may be deciduous or persistent, and their 

 number, varying from three upwards, indicates the number of 

 leaves forming the united whorl. 



89. Stomata (77) are distributed along the valleculae either 

 irregularly or disposed in ranges on either side of the valleculae. 

 The epidermis frequently contains much silica, and the rough- 

 ened tubercles of some species give the surface a harsh feeling. 



90. Fructification. The fructification in Equisetum is 

 arranged in cone-like spikes borne at the apex of the fertile 

 stems. These spikes are composed of successive closely-placed 

 whorls of shield-shaped, stalked scales or modified leaves, each 

 of which bears from five to ten one-celled sporangia on its under 

 side. The sporangia open along the inner side to discharge 

 their numerous spores, whose outer coat is spirally split into 

 two bands, forming the so-called elaters. The elaters when dry 

 are spread out at right angles to each other in the form of a 

 cross, and probably assist in scattering the spores ; when moist 

 they rapidly absorb water, and become closely coiled around the 

 spore.* 



91. Germination. The spores of Equisetum retaining 

 their powers of germination only a few days, soon develop 

 branched and irregularly lobed prothallia, which are provided 

 with chlorophyll. These are usually dioecious, the male being 

 smaller, and producing antheridia at the end or margin of the 

 larger lobes. The antherozoids are large, and provided with a 

 peculiar appendage known as the "float." The female prothal- 

 lium may reach one half inch in length, and develops archegonia 

 on the anterior margin of the fleshy lobes. The process of 

 fertilization is similar to.that of ferns. 



* An interesting illustration of this can be seen by placing a mass of fresh 

 spores on a slide uncovered, and examining it with a low power. By breath- 

 ing on the slide the elaters coil closely about the spore ; as soon as the moist- 

 ure evaporates they uncoil, and in their activity jostle each other in great 

 confusion. 



