Chap III.] DOWNWARD GROWTH OF THE ROOT. 
99 
ends, and to their not being thrust bodily- 
through the earth. I have laid horse-chestnuts 
on the surface of a box of earth, and, by arching 
them over with layers of damp flannel which 
did not touch them, they grew, and the tap¬ 
roots struck downward into the earth and fixed 
themselves; though they had no foreign fulcrum 
to press from, except the weight of the seed, which 
was not perpendicularly above them. Can there 
be anything glutinous about the silver ends of 
roots, which enables them to adhere to the earth 
while their new growth is protruded through it ? 
And I may ask here, if roots have spongioles or 
small sponges at their ends, are we to believe 
that these sponges are locomotive or stationary? 
Are we to believe that these delicate organs are 
thrust forward through the hard ground ? Or, 
are we to suppose that the perpetual new growth 
of root is perpetual new sponge, as its preceding 
sponge is converted into root ? 
As the stems of the plants grew, I heightened 
the moist canopy, and let in light only by one 
opening. All the stems grew towards that 
opening : and as often as the opening was, 
changed from one end of the canopy to the 
other, the direction of the stems was changed; 
H 2 
