198 BOTANY. 
x 
or moist earth, enlarging and successively dividing until a 
flattish irregular plant (the first stage, or prothallium) a 
few millimetres in breadth 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 (Equisetacee) of living plants, 
including a single genus and twenty-five 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 
Rash, called also Dutch Rush (E. hiemale), with harsh green branch- 
less stems which produce cones, and survive the winter. 
