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sleep, they have no need of sleep,—nor would you if, 
like the tulip, you remained all day waving gracefully 
upon a stalk! Perhaps the flowers close to keep warm 
on cold nights, perhaps they try to avoid the dew, or 
maybe they want to save their pollen from being spoiled 
by rain in wet weather. 
The only movement which most plants can make is this 
closing of their petals when the dark comes, but in tropi¬ 
cal countries there can be found a prickly shrub the 
leaves of which close when touched. For this reason it 
is called the Sensitive Plant; it grows a few feet high, 
bears purple flowers, and people like to cultivate it in 
hothouses to watch the leaf stalks droop and the leaf¬ 
lets fold up the minute it is touched. We do not know 
exactly why the Sensitive Plant has this power of move¬ 
ment, it does not frighten away browsing animals or 
other enemies, and repeated movements seem to tire the 
plant so that it becomes stunted in its growth, like a 
growing boy who is forced day after day to overwork 
his heart or his muscles. 
There are other plants, however, to which the power 
of movement means a great deal—it means their dinners 
and their suppers ! Not all plants live upon air and water 
like the rose, or feed upon their host as the mistletoe 
feeds upon the oak. Some plants live upon insects, and 
these they catch and kill by means of leaf movements. 
