CH. VIII.] THE DISEASES OF PLANTS. 253 



themselves towards the same small orifice admitting 

 a few illuminating rays. 



Almost every flower has a particular degree of 

 light requisite for its full expansion. The blossoms 

 of the pea and other papilionaceous plants, spread 

 out their wings in fine weather, to admit the solar 

 rays, and again close them at the approach of night. 

 Plants requiring powerful stimulants do not expand 

 their flowers until noon, whilst some would be de- 

 stroyed if compelled to open in the meridian sun — of 

 such is the night-blooming Cereus, the flowers of 

 which speedily droop, even if exposed to the blaze of 

 light attendant on Indian festivities. 



From these and other facts incidentally mentioned 

 in the preceding chapters, without belie"STng that 

 the}' demonstrate sensation to exist in plants as acute 

 as that possessed by the superior or more perfect 

 classes of animals, yet they certainly are satisfactory 

 e\ddence that plants possess it to a degree nearly as 

 high as that with which the zoophytes, or even the 

 polypus and leech, are gifted. Some of these ani- 

 mals may be cut into pieces, and each section will be- 

 come a perfect individual ; of others, their heads 

 being taken off, may be grafted upon other bodies ; 

 and a third class of them may be turned with their 

 insides outwards, without any apparent inconvenience. 

 If plants be endowed with no more or even less sens- 

 ation than must be that of such animals as these, it 



