198 BOTANY. 



or moist earth, enlarging and successively dividing until a 

 flattish irregular plant (the first stage, or prothallium) a 

 few millimetres in Ibreadth is produced. This stage is 

 short-lived. It bears sexual organs upon its edges or lobes; 

 in some cases both kinds of organs are on the same plant, 

 •while very commonly they are upon separate plants. 



415. The antherids consist of one or more cells, sur- 

 rounded by a layer of cells. The inner cells divide inter- 

 nally into many sperm-cells, each of which contains a large 

 spirally twisted antherozoid. 



416. The archegones are flask-shaped organs sunken into 

 the tissues of the plant. At maturity the neck is open 

 down to the roundish germ-cell. Fertilization takes place 

 in water, the antherozoids swimming by means of their 

 many cilia to and down the neck of the archegone, where 

 they unite with the germ-cell. 



417. After fertilization the germ-cell begins to divide 

 again and again, soon giving rise to a new plant of the 

 second stage. The latter is at first a small and quite sim- 

 ple stem with minute leaves, but the successive joints be- 

 come larger and larger until full size is reached. At the 

 same time roots develop which push downwards into the 

 soil, absorbing moisture and nutritious solutions. 



This class contains but one order (Equisetacese) of living plants, 

 including a single genus and twenty-flve species. Among the more 

 well known are the Common Horsetail (Equisetum arvense), which 

 sends up short-lived, pale or brownish cone-bearing stems in spring, 

 and profusely branching green stems in summer (E. telmateia, the 

 Great Horsetail of Europe and our own Northwestern region, re- 

 sembles, but is larger than, the Common Horsetail); the Woodland 

 Horsetail (E. sylvaticum), whose green cone-bearing stems branch 

 profusely after fruiting, and persist all summer; and the Scouring 

 Rush, called also Dutch Rush (E. hiemale), with harsh green branch- 

 less stems which produce cones, and survive the winter. 



