ARCHE GONIATE S 115 



bears antheridia and archegonia on its under surface embedded in its 

 tissue. The sporophyte usually bears the spores on the under surface 

 of undifferentiated leaves. The sporangia are stalked and grouped in 

 clusters (sori) . The sori are often covered by a scale (indusium) . 



286. Order 4. The Hydropteridece or water-ferns, are a small group of 

 plants which bear little resemblance to common ferns. Some grow in 

 the mud, partly submerged, others float on the surface of the water. 

 They are of special biological interest because the sporophyte bears two 

 kinds of spores, small " microspores " and large "megaspores." The 

 microspores develop a very simple prothallus consisting of only a few 

 colorless cells, and a few antheridia. The megaspores develop a slightly 

 larger prothallus which, however, only projects slightly beyond the broken 

 sporangium wall. (A megasporangium produces only one megaspore.) 

 A few archegonia are formed in the prothallus but only one egg cell devel- 

 ops. The microspores therefore develop male gametophytes and the mega- 

 spores female. 



287. Class 2. Equisetinae. This class contains only one 

 genus, Equisetum, the common scouring rush or "horse-tail." 

 These plants have an underground stem from which the erect 

 fruiting and vegetative stems rise each season. The stem is 

 fluted and jointed and green since there are no foliage leaves. 

 The scale leaves sheathe the stem at the nodes. The fruiting 

 stems are usually simple while the vegetative stems bear whorls 

 of branches at the nodes. The epidermis is encrusted with 

 silica which gives the stem a harsh feel and lends the name 

 scouring rush. The fruiting stems bear a conical spike of 

 umbrella-shaped sporophylls. The spores are all of one kind 

 and are each provided with four ribbon-like hygroscopic appen- 

 dages (elaters) by which the spores are scattered. The spores 

 give rise to a branching prothallus which is usually unisexual. 



288. Class 3. Lycopodinae. The Lycopodinae are small 

 plants with some affinities to the ferns but of very different 

 appearance. The sporophylls each bear a single sporangium. 



289. Order i. The Lycopodiacece are the lycopodiums, "trailing cedar" 

 or "ground pine." The stem is usually trailing, with short ascending 

 branches. Branching of stem and roots is dichotomous. The leaves are 



