27° BOTANICAL GAZETTE [OCTOBER 
COMMON BEAN (GARDEN PLANTS) 
Twenty-four plants of the common bean were selected and 
placed under experimental conditions. The longitudinal com- 
pression was localized in the lower parts of the stems by means 
of the pieces of bamboo. Measurements and comparisons showed 
no greater gain in mechanical tissue in the experimental plants 
than in the control plants. 
Discussion 
The question of growth and increase of mechanical tissue with 
special reference to compression may be considered under five 
heads: (r) heredity and variation; (2) correlation; (3) mechanical 
effects of compression; (4) stimulatory effects of compression; 
(5) compression in connection with other stimuli. 
HEREDITY AND VARIATION 
The production of a certain amount of mechanical tissue in 
plants is a specific characteristic just as much as is the production 
of leaves of certain form. Just as leaves of a given species may 
vary in number and size under the laws of fluctuating variability, 
so may the amount of mechanical tissue vary. Entirely independ- 
ent of any known cause, sudden variations may occur in the amount 
of mechanical tissue formed. The best illustration of this sudden 
variability is furnished by Oenothera lata (DE VRIES 9), 4 mutant 
which does not produce enough mechanical tissue to support a 
own weight. Another common illustration is furnished by certamm 
laciniate-leaved varieties of the sumach, which have stems too 
weak to bear their own weight. The difference in the amount 
of xylem in closely related forms is shown in many grafts. When 
a scion of one species of elm is grafted upon another species OF 
variety, it soon becomes larger than the branch upon which it was 
grafted, although there is more mechanical strain upon the branch 
than upon the scion. The same phenomenon is frequently see? in 
grafts upon fruit trees. 
All of my experiments, especially those in which the weight o! 
the plants was counterbalanced, showed that it is characteristic 
of each of the species to produce a certain amount of mechanical 
