Sept, i, 1921 
873 
Growth in Branches of Young Pear Trees 
It would also appear that the data fail to support the assumption that 
in such cases a growth-stimulating substance migrates from the sur¬ 
rounding tissues and accumulates in the dominant area. It is quite 
probable that the growth-stimulating substances are of the nature of 
catalysts but that they occur in all buds on a mother shoot. We know 
that the amputation of a portion of a pear shoot will be followed by the 
growth of laterals from the buds immediately below the point of ampu¬ 
tation {id). The data here presented show that the first laterals from 
the shorter mother shoots were longer than those from the longer mother 
shoots. Yet the latter had a larger surrounding area to draw upon if we 
assume that the growth of laterals was governed by the migration of 
growth-promoting substances. Furthermore, the slope of the regression 
line (fig. 6) indicates that the relationship between length of mother 
shoot and length of first lateral is negative throughout the whole 
population. 
In order to remove a possible confusion in the mind of the reader, 
the substance of previous paragraphs may be repeated at this point! 
The shorter mother shoots, although producing longer apical laterals, 
nevertheless produced practically the same total of laterals as the longer 
mother shoots. 
It would seem more logical to assume that each of the buds on the 
mother shoot is provided with the growth-stimulating substance (catalyst) 
and that all will grow provided they are sufficiently freed from sub¬ 
stances which inhibit the action of the catalyst. 
SUMMARY 
(1) The paper contains an attempt to analyze and correlate the 
growth phenomena of young shoots on branches of the pear tree 
(2) Mother shoots which had been headed back in the previous winter 
produced about 65 per cent greater total growth of laterals than their 
unpruned neighbors. The frequency distributions of laterals on both 
classes of mother shoots show a positive skewness, which is taken to 
indicate a tendency to produce more than the mean quantity of wood. 
(3) If mother shoots received any pruning whatsoever, the severity 
of the pruning seemed to have little influence upon the total amount of 
new laterals produced in the following season. The growth response 
showed little tendency toward a “restoration of lost parts.” 
(4) The longest lateral on a mother shoot is usually at the distal end 
and each successively lower lateral is usually shorter than the one above 
it. The mathematical relationships of the system of laterals indicate a 
• C ™ lte functlona l elation of the growth processes involved. Variability 
in e length of laterals tends to increase as their distance from the 
distal end of the mother shoot increases. 
54131°—21 -6 
