136 STUDIES IN GENERAL PHYSIOLOGY 
which they are brought in contact, no matter how long one 
may wait; while, on the other hand, this reaction is always 
obtained with certainty in growing roots. I have also 
assured myself of the fact that when adventitious roots are 
brought in contact with the wall of a beaker, they imme- 
diately attach themselves to it, and grow on its surface. 
11. As soon as a root comes in contact with a solid body, 
it grows rapidly in length, and in a few days exceeds the 
length of other newly formed and equally long roots, which 
are prevented from contact with solid bodies.’ 
The attachment of the root to a solid body influences form 
in a second direction. While we observed above that new 
stems grow from the upper surface of a root when it is sur- 
rounded on all sides by water, we find, when the root is 
attached to a solid substratum, that the stems arise from that 
surface of the root which lies opposite the solid body. In 
their further development these stems also grow only straight 
upward, though not entirely vertically. 
12. I have observed in the roots of Aglaophenia a phe- 
nomenon relative to growth which has thus far been known 
only in plants. 
The longitudinal growth of the root is confined to a nar- 
row region situated near the tip (while no longitudinal 
growth occurs in the remaining portions of the root). This 
could be shown in the following way: I permitted the roots 
of Aglaophenia to attach themselves to a slide and grow 
upon it. A slight bulging out soon occurred just behind the 
tips—the beginning of a new stem, which on the next day 
reached a length of 3mm. and soon thereafter bore polyps. 
I marked the position of the beginning stem on the glass, 
by etching a line into the glass. The position of this new 
1 DALYELL observed in Sertularia halecina that new growths occur which 
adhere to other solid bodies and thereby become abnormally long. ‘‘These com- 
ing in contact with a solid surface have a tendency to adhere and to extend in 
irregular prolongations surpassing the natural increment,” Rare and Remarkable 
Animals of Scotland (London, 1847), p. 165. 
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