HORSE TA ILS. 283 



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 un- 

 branched, 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. 



577. Gametophyte of equisetum. The spores of equisetum have chloro- 

 phyll 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 pro- 

 thallium (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 reproductive 

 organs, and the phases and fruiting of the plant, are more essential in deter- 

 mining relationships of plants than the mere outward appearances. 



