172 



ABOUT HORSETAILS, 



[CHAP. 



These latter are evidently antheridia. The larger 

 spores germinate by division of the cells of the apex, 

 from which archegonia are formed. Fig. 130 repre- 

 sents a leaf with its spore-case, which is also shown 

 detached. Fig. 131 is a section of the spore-case 

 showing the three chambers jnto which it is divided. 

 The plant is rare in the south of England. The 

 name is derived from two Greek words, Isos, equal, 

 and etos, a year, in allusion to its leaves, which are 

 persistent during the whole year. 



The remaining species is known as Pilularia globu- 

 lifera, the Pillwort, or Pepper-grass. It grows on 

 the margins of ponds and lakes, 

 and presents the appearance of 

 fig. 132. It has a creeping stem, 

 from which, at intervals, are given 

 off the fibrous roots which fix it 

 in the mud, and the small quill- 

 like leaves. These leaves are at 

 first rolled up in a circinate man- 

 ner, like the fronds of ferns, and 

 vary in length from an inch to 

 four inches. They are hollow, 

 bright green, and smooth. 



The spore-cases are attached by 

 a short stalk to the stem, at the 

 base of the leaves. They are 

 about the size of a pepper-corn, 

 from which fact the popular name has arisen ; they 

 are densely clothed with hairs, and, when ripe, split 

 open into four valves, to the centre of which the 

 spores and antheridia are attached. The lower part 



FIG. 132. 



