810 Movements of Plants. 



ried to the upper side of those at a little distance, and thus the 

 neighboring leaflets are also depressed. The depression of the 

 veins upon the mid-rib, and of the mid-rib or foot-stalk itself 

 upon the stem, will follow in like manner ; the extent to which 

 the movement is propagated, being dependent on the amount 

 of fluid expelled from the lower side of the intumescence, in 

 the parts where it has already taken place. 



Various other stimulants besides the touch of a hard sub- 

 stance, will produce similar effects. Thus, if electric sparks 

 be communicated to the lower side of the intermescence, or the 

 rays of the sun be concentrated on it with a burning-glass, a 

 similar contraction of its vesicles, and depression of the leaf 

 will follow. In all these cases, the leaves return after a time 

 to their usual condition. Several species of the Acacia tribe 

 growing in warm climates, exhibit corresponding changes in a 

 less degree. The closure of the fly-trap of the Dionaea, may 

 be probably explained on similar principles. The part here 

 irritated is the tissue at the base of the three thorns on each 

 side of the leaf, one of which must be touched in order to ex- 

 cite the movement. 



THE FERN TRIBE. 



FROM LINDLET. 



Ferns are the most completely organized of Flowerless 

 plants, and approach nearer than any others to the Flowering 

 tribes. In the northern parts of the world, they are green, 

 leafy productions, which die down to the ground every year; 

 and they are seldom more than two or three feet high. But in 

 tropical countries many of them far surpass these pigmy dimen- 

 sions ; they acquire real trunks, resembling those of palms, and 

 often rise to the height of forty or fifty feet without a leaf. 

 Even a more considerable stature is spoken of by travellers. 

 At all times they are graceful objects, from the slender stems 

 on which they bear their leaves, which wave in the breeze like 

 plumes of feathers, and from the multitude of leaflets into which 



