36 FIRST FORMS OF VEGETATION. 
motion; while the slightest moisture of one’s 
breath invariably causes the little teeth instantly 
to close over the mouth. This extremely simple 
mechanism is one of the most wonderful contri- 
vances of Nature, one of the most extraordinary 
adaptations of means to an end, to be found in 
the whole economy of vegetation. Within the 
capsule the seeds surround a slender pillar or colu- 
mella, and are enclosed in a membranous bag. 
The seta or fruit-stalk is in some mosses terminal, 
and in others lateral, springing from the top of the 
stem or the side, and these characters afford a 
convenient mode of arranging the whole tribe into 
acrocarpi or pleurocarpi. Mosses with terminal 
fruit-stalks are more fugacious, and may be re- 
garded as analogous to spring or annual plants 
whose blossoms are produced at the summit of 
the stem or direct from the root ; while mosses 
with lateral fruit-stalks are more permanent, and 
may be compared to perennial plants, shrubs, 
or trees, whose blossoms or fruit appear on side 
sprouts or branches, and are concealed among 
the foliage. Elevated as the seed-vessels are by 
their stalks, they are freely exposed to the ripen- 
ing effects of sun and wind; and it is a curious 
sight to see these straight footstalks gradually 
bending, reversing the seed-vessels, and empty- 
ing the seeds they contain as from a pitcher, 
