]24 
ORGANOGRAPHY. 
BOOK I. 
character in their organisation to show which of their faces is 
destined to become the upper surface, and which the under. 
For the purpose of ascertaining whether there existed any 
natural but invisible predisposition in the two faces to undergo 
the changes w^hich subsequently become so apparent, and by 
means of which their respective functions are performed, or 
whether the tendency is given by some cause posterior to their 
first creation, the following experiments were instituted : — 
Five bulbs were sown upon powdered sandstone, and it was 
found that the face which touched the sandstone produced 
roots, and the opposite face formed stomates. It was, how- 
ever, possible that the five bulbs might have all accidentally 
fallen upon the face which was predisposed to emit roots ; 
other experiments of the same kind were therefore tried, first 
with eighty, and afterwards with hundreds of little bulbs, — 
and the result was the same as with the five. This proved 
that either face was originally adapted for producing either 
roots or stomates, and that the tendency was determined 
merely by the position in which the surfaces were placed. 
The next point to ascertain was, whether the tendency once 
given could be afterwards altered. Some little bulbs, that had 
been growing for twenty-four hours only, had emitted roots ; 
they were turned, so that the upper surface touched the soil, 
and the under was exposed to light. In twenty-four hours 
more the two faces had both produced roots : that which had 
originally been the under surface went on pushing out new 
roots ; that which had originally been the upper surface had 
also produced roots : but in a few days the sides of the young 
plants began to rise from the soil, became erect, turned over, 
and finally recovered in this way their original position, and 
the face which had originally been the uppermost immediately 
became covered with stomates. It, therefore, appears that, 
the impulse once given, the predisposition to assume particular 
appearances or functions is absolutely fixed, and will not 
change in the ordinary course of nature. This is a fact of 
high interest for those who are occupied with researches 
into the causes of what is called vegetable metamorphosis. 
The parenchyma is, if casually examined, or even if viewed 
in slices of too great thickness, apparently composed of heaps 
