324 Life and Immortality. 
some plants, there can be no doubt that it is it that affords 
the radicle some slight assistance in penetrating the ground. 
But whether or not a radicle, when surrounded by softened 
earth, is aided in making a passage for itself by circumnu- 
tating, one thing is certain, that is, that this movement, by 
guiding the radicle along a line of least resistance, can hardly 
fail to be of high importance. Should, however, a radicle in 
its downward growth break obliquely into any crevice, or an 
opening left by a decayed root, or one made by the larva of 
an insect, and more especially by worms, the circumnutating 
movement of the tip will materially aid it in following such 
open passages. Not only our own observation, but also those 
of such eminent authorities as Darwin and Hensen, conclu- 
sively show that roots commonly run down the old burrows 
of worms. 
But radicles of seedlings, as well as those of more vigor- 
ous plants, would pass over stones, roots and other obstacles, 
which they must necessarily encounter in the soil. This 
they are abundantly able to do, for they are exceedingly 
sensitive just above their apices, and bend like a tendril 
towards the touching object. When, however, one side of 
the apex is pressed by any object, the growing part bends 
away from that object, and this seems a beautiful adaptation 
for avoiding obstacles in the soil, and for following the lines 
of least resistance. 
So feeble is the circumnutating movement of the terminal 
growing part, both of the primary and secondary radicles, 
that it can assist them but little in penetrating the ground, 
excepting when the superficial layer is very soft and moist. 
But it must aid them materially when they chance to break 
obliquely into cracks, or into burrows that have been made 
by earth-worms or larve. Moreover, combined as it is with 
the sensitiveness of the tip of the radicle to contact, it can 
hardly fail to be of the highest importance, for as the tip is 
always endeavoring to bend to all sides, it will press on all 
sides, and will thus be able to discriminate between the 
