TRE eae re Nt ee RET Me eT tT. OR LEN Oe el emeemeaet En Ty 
Botany and Zoology. 247 
duced by the changing turgescence of the cells on different sides 
of a stem or footstalk, which may or may not be fixed by conse- 
quent growth or solidification. This Mr. Darwin, we presume 
rightly, concludes to be the faculty or susceptibility upon which 
heliotropism, geotropism and the like (not to speak of aphelio- 
other words, upon which the solar rays and some occult influence 
of the earth—act, modifying the sweeps or converting them into 
forth and back or other special movements. Among these, that 
fly 
im most mature plants. This should needs be, since, as Mr. 
g i 
medium in which it is developed, one would not look there for 
the endowments which Mr, Darwin finds in it. But this root-tip 
that 
va root exhibits three kinds of movement ; first that of circum- 
0 : " : 
the harder and softer adjoining surfaces, . . . and to bend from 
the harder soil and follow the lines of least resistance,” so modi- 
