CURRENT LITERATURE 
NOTES FOR STUDENTS 
Quantitative relations of regeneration. —ReeEp' has contributed a new 
quantitative study of growth in pruned trees as compared with unpruned, 
with particular reference to sich questions as whether the growth response ~ 
is merely the restoration of lost parts, in what manner the amount of regenera- 
tion is correlated with length, and number of buds of the mother shoot; also 
what light these relations afford in the problem of the dominance of the shoot 
apex. He finds no correlation between the length of mother shoots and the 
amount of new growth produced by them, whether pruned or unpruned. On 
the other hand, shoots pruned the previous winter produced about 65 per cent 
more total growth than comparable ‘unpruned shoots; the degree of heading 
back had little effect on the amount. Hence, regeneration following pruning 
is not a tendency to restore lost parts, but in terms of growth rate of the shoot 
is taken to indicate increased activity of the growth catalyst. In connection 
with the characteristically greater growth of laterals at the distal end of a 
pruned shoot, the conclusion is reached that this greater activity results from 
the elimination of the growth-inhibiting chalones produced in the apical part 
of the shoot which normally keep the lateral buds in dormancy. The alter- 
native hypothesis that pruning reduces the number of potential growing 
points, hence permits of greater development of the remaining buds, is rejected 
because it was found that the more heavily pruned mother shoots, that is, 
the shoots in which the number of remaining buds was least, failed to make 
more total lateral growth than the longer mother shoots. It is worthy of note 
that according to the author’s hypothesis of basipetal migration of a growth- 
ibiting substance, ‘the greatest concentration, and hence the most pro- 
nounced inhibiting effect, is at the base of the shoot. When a mother shoot 
is pruned to a few basal buds, however, the laterals developing from such buds 
become longer than laterals of less severely pruned shoots. This would seem 
to be evidence indicating some effect from reduction of competition between 
the several buds. 
Lors? reaches a somewhat different conclusion from experiments on 
regeneration in Bryophyllum, in which the weight of shoots produced from the 
*Reep, H. S., Correlation and growth in the branches of young pear trees. 
Jour. Agric. Res. 21:849-876. pl. r. 1921. 
2 LoEB, JACQUES, The quantitative basis of the polar character or er in 
Bryophyllum. ee ee §21-522. 1921. 
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