8o The Natural Abscission of Twigs. 
point that the terminal bud is the first to open in 
spring). 
(d) Order of fall of lateral branches along the length of a 
year’s extension growth. 
(e) The order in which, in the transition to the flowering 
stage, the buds pass into the reproductive phase. The 
most vigorous buds in the axils of the biggest leaves 
are the first to change from leaf -bearing to catkin - 
bearing buds. 
If a second year twig is examined, it is usual to find that 
the lowermost buds have been so small that they have remained 
dormant, that those immediately above have grown out into 
lateral branches, which are weak (being derived from relatively 
small buds and having grown out relatively late) and have 
made very insignificant growth, whilst the most vigorous 
and well developed shoots are to be found a little above half 
way up the shoot. (Fig. i.) If a comparable region is 
examined over a number of annual growth increments, it is 
found that the lower branches, which made poor growth, are 
shed — usually in almost regular sequence, until finally only 
one or two (or occasionally none) of the most vigorous laterals 
have resisted the abscission process, these being situated a 
little beyond half way along the extension growth of the 
particular year’s growth. So characteristic is the distribution 
of the laterals that a reasonably accurate estimate of the age 
of a branch system may be obtained by counting the number 
of groups of (or single) laterals separated by a length of axis 
free from laterals. 
When the trees are about 20-25 years old the upper 
branches begin to flower. The change is gradual and at first 
only one or two of the buds may be catkin-bearing on an 
otherwise vegetative shoot. The catkin buds can be recognised 
from the lateral vegetative buds by their larger size. They 
are also relatively shorter and fatter. The terminal bud is 
about the same size as the catkin buds, but in all cases remains 
vegetative. Another feature associated with the development 
of a catkin bud is that the leaf cushion of the subtending leaf 
is more swollen, so that the cylindrical bud comes to be 
situated on a relatively wide notch, on which a circular scar 
is left when the catkin falls. The vegetative buds are more 
closely adpressed to the stem and are attached by a narrower 
base, which is much less conspicuous than that of the catkin 
bud. As more and more of the buds become reproductive 
this seating of the scar above a swollen cushion gives the 
twigs a very different appearance from the vegetative. The 
catkin-bearing twigs appear stouter and more irregular in 
outline and are also more rigid than the long pliable vegetative 
shoots. In the final stage of a reproductive twig, catkin buds 
The Naturalist 
