1895. ] Regulatory Formation of Mechanical Tissue. 445 
results in similar experiments on trees as well as mine on 
several herbaceous and shrubby plants point to the same con- 
clusion. Knight’s result on removing the outer dead part of 
the bark and de Vries’ on making longitudinal slits in the cor- 
tex of trees should be referred to irritability and border 
closely upon regulatory action. Krabbe showed conclusively 
that the xylem formed subsequently to slitting in the autumn 
is not spring wood as de Vries thought. It is aresponse made 
to the injury of the knife. 
The excentricity of branches and roots considered by Kraus 
and made much of by Detlefsen does not conform to the rules 
laid down by these two authors. I have found that the 
strongest development of tissue is often present on the con- 
vex side, but often also on the concave side. Gladiolus com- 
munis is an example of a plant forming an excess of tissue on 
the convex side of a geotropic curvature of the stalk, while 
Atlanthus glandulosus Desf. furnishes an example of exces- 
sive growth on the concave side. Detlefsen stated that hor- 
izontal branches have the greatest development on the lower 
side. In the Quince (Pirus cydonia) I have found it greatest 
on the upper side. Moreover a branch that in part of its ex- 
tent is convex upward, and, farther out, convex in the oppo- 
site direction, does not change its excentricity with the 
change of curvature. If this statement does not hold true for 
all plants, it does for many, as my own observations have con- 
vinced me. According to Detlefsen’s rules, the buttresses 
which extend on the trunk of a tree from the base of the 
branches downward and from the roots upward ought to re- 
verse their position. : 
If we refer these variations to phenomena of regulation, we 
have a theory that is tenable; for one plant may regulate in 
regulatory formation. What better illustration could be de- 
sired? What greater need of strengthening itself could a 
plant feel? 
Another case of regulatory growth is furnished by the be- 
havior of climbing organs as determined by Darwin’? and. by 
Cause such an organ to grow free from contact 
1° Darwin, Climbing Plants 48, 50, 51. 1876. 
*Treub, Ann. du Jard. Bot. de Buitenzorg 2: —. 1882. 
