Chap. III.] DOWNWARD GROWTH OF THE ROOT. 
105 
in the nature or cellular organisation of the 
original first or tap-root of seedlings, as com¬ 
pared with that of their branch-roots : though 
I cannot guess by what agent the growth of the 
differing structure of the tap and branch-root is 
to be directed in their differing course, any more 
than I can guess the agent which determines the 
upward growth of the first gemmule of a seed¬ 
ling while it is in the earth, and before it reaches 
the light. 
Still farther to test this idea, which these 
experiments gave me, — that first or tap-roots 
alone would appear below, and that no branch- 
roots would do so,—in March, 1846, I placed 
cuttings of gooseberry and currant in a pot of 
earth inverted on wire, and suspended in the 
air. The cuttings struck, and no roots appeared 
below; the cause being, as I conceive, that, as 
there were no seedling-roots, so there were no 
tap-roots. In July I destroyed all the cuttings 
except one currant, placed the experiment on a 
support from below, and removed the flower-pot. 
There were a great many roots growing in all 
directions round and over the outside of the ball 
of earth. I replaced the flower-pot with a large 
chimney-pot, which I filled with earth. In 1847 
the main shoot of the currant slip was 4 ft. 1 in. 
