HORSE TA ILS. 28 1 



Curious as it may seem, these are the leaves of the horsetail. 

 The stem, if we examine it farther, will be seen to possess numer- 

 ous ridges which extend lengthwise and which alternate with 

 furrows. Farther, the ridges of one node alternate with those 

 of the internode both above and below. Likewise the leaves 

 of one node alternate with those of the nodes both above and 

 below. 



573. Sporangia. The end of this fertile shoot we see pos- 

 sesses a cylindrical to conic enlargement. This is the fertile 



spike, and we note that its surface is marked off 

 into regular areas if the spores have not yet been 

 disseminated. If we dissect off a few of these por- 

 tions of the fertile spike, and examine one of them 

 with a low magnifying power, it will appear like the 

 fig. 322. We see here that the angular area is a 

 Fig. 322. disk-shaped body, with a stalk attached to its inner 

 phyf/oVequSetum surface, and with several long sacs projecting from 

 Ing^p^ngiaTn its inner face parallel with the stalk and surrounding 

 the same. These elongated sacs are the sporangia, 

 and the disk which bears them, together with the stalk which 

 attaches it to the stem axis, is the sporophyll, and thus belongs to 

 the leaf series. These sporophylls are borne in close whorls on 

 the axis. 



574. Spores. When the spores are ripe the tissue of the 

 sporangium becomes dry, and it cracks open and the spores fall 

 out. If we look at fig. 323 we see that the spore is covered 

 with a very singular coil which lies close to the wall. When the 

 spore dries this uncoils and thus rolls the spore about. Merely 

 breathing upon these spores is sufficient to make them perform 

 very curious evolutions by the twisting of these four coils which 

 are attached to one place of the wall. They are formed by the 

 splitting up of an outer wall of the spore. 



575. Sterile shoot of the common horsetail. When the 

 spores are ripe they are soon scattered, and then the fertile 

 shoot dies down. Soon afterward, or even while some of the 

 fertile shoots are still in good condition, sterile shoots of the 



