224 Stone : The power of growth of ostrich ferns 



turing the concrete. This substance was so hard that after it had 

 been pushed up it was impossible to make any impression upon 

 the ragged edges except by the use of tools. The fern fronds, 

 when pushed through the concrete, were practically unscarred 

 in all cases and were normal in shape. The work was accom- 

 plished by a slow and constantly increasing pressure exerted on 

 the under surface of the concrete. 



There are many instances on record showing the great power 

 exerted by plants when growth is restricted. It is well known 

 that such restriction acts as a marked stimulus to the osmotic 

 properties of the cells. Pfeffer"^ and others have measured the 

 power of gro\\i:h in various plant organisms, and in one instance 

 Pfeffer records a longitudinal pressure equal to 24 atmospheres in 

 the roots of Zea Mays^ when encased in plaster of Paris. The 

 writer has observed many instances where considerable power has 

 been exerted by plants in overcoming difficulties. He has 

 occasionally observed mushrooms breaking through tar concrete 

 walks near dwellings, in which instance much power was exerted 

 by these most delicately constructed plants. Cases are on 

 record where flagstones have been dislocated by mushrooms 

 which grew under them. We observed also in one instance a 

 large dwelling house with one corner elevated a few inches above 

 the others by the presence of elm roots under the foundation, and 



the dislocation of sidewalks, curbings, etc., by tree roots is a 

 matter of common observation. 



There are innumerable instances seen in mountainous regions 

 where the roots of trees growing among ledges and boulders have 

 moved large masses of rock. The writer has had under observa- 

 tion for many years a black birch tree, one of whose roots is con- 

 tinually elevating a large boulder. This particular tree has been 

 growing in this situation for many years and one of the roots has 

 entered a fissure in the boulder. This crack or fissure is at an 

 angle of about 15 degrees, and where the root passes between the 

 two halves of this boulder its vertical diameter is 4 or 5 inches, 

 while its lateral diameter is 18 or 20 inches or more. Careful 

 measurements of the dimensions of this boulder, together with 

 specific gravity determinations, would indicate that the weight is 



^■■" '" — " ' ^ — ^ — ~" " ■^—^^p^Bi I ^^ ^^ — I -- - ■ — p,— . ^ 



* ** Druck und Arbeitsleistung durch wachsende Pflanzen," 1893. 



