178 BOTANY. 



on wet banks, or in sandy soil which contains moisture along 

 railroad embankments. It is the scouring rush (E. hyemale), so 

 called because it was once used for polishing purposes. This 

 plant like all the species of the horsetails has underground stems. 

 But unlike the common horsetail, there is but one kind of aerial 

 shoot, which is green in color and fertile. The shoots range as 

 high as one meter or more, and are quite stout. The new 

 shoots which come up for the year are unbranched, and bear 

 the fertile spike at the apex. When the spores are ripe the 

 apex of the shoot dies, and the next season small branches may 

 form from a number of the nodes. 



293. Gametophyte of equisetum. — The spores of equisetum 

 have chlorophyll when they are mature, and they are capable 

 of germinating as soon as mature. The spores are all of the 

 same kind as regards size, just as we found in the case of the 

 ferns. But they develop prothallia of different sizes, according 

 to the amount of nutriment which they obtain. Those which 

 obtain but little nutriment are smaller and develop only 

 antheridia, while those which obtain more nutriment become 

 larger, more or less branched, and develop archegonia. This 

 character of an independent prothallium (gametophyte) with 

 the characteristic sexual organs, and the also independent 

 sporophyte, with spores, shows the relationship of the horsetails 

 with the ferns. We thus see that these characters of the repro- 

 ductive organs, and the phases and fruiting of the plant, are 

 more essential in determining relationships of plants than the 

 mere outward appearances. 



