214 Barratt* — A Contribution to our Knowledge of the 
Origin of Lateral Buds. 
The primary axis only gives rise sparingly to lateral buds, but as the 
successive aerial axes develop, they produce whorls of branches. These 
arise from .buds which have been clearly demonstrated to be of exogenous 
origin (6, 8) and to occur in the axil of the leaf-sheaths, alternating in 
position with the leaf-teeth. 
The tracheides of the bud internodes follow exactly the same order of 
development as those of the primary axis, i.e. the internodal elements 
become lignified first and are linked up with the leaf-traces and with the 
corresponding elements of 
higher internodes later by the 
short tracheides of the node. 
The junction of the bud 
vascular system with that of 
the parent stem is brought 
about by the formation of a 
closed tube of short, strongly 
thickened elements repeating 
the structure already described 
which is found at the base of 
the secondary axis. 
Rhizomes . The first rhi- 
zomes arise as lateral buds at 
the base of young aerial stems. 
In E. avvense they appear, as 
a rule, after three or four up- 
right shoots have been formed 
but this is dependent upon con- 
ditions of growth, as already 
stated. 
A rhizome is like an aerial shoot except with regard to its direction of 
growth and its lack of chlorenchyma. Where the plants are left crowded 
together these rhizomes have not so good a chance of developing, and their 
growth may consequently be arrested. Towards the end of the summer 
other shoots grow out as short fat tubers (PI. VI, Fig. i, £,/). These tubers 
in the young plant consist only of one long swollen internode crowned by 
a small node and terminal bud, although in older plants a chain of tubers 
may be formed by the development of successive internodes. . 
There is a striking difference in structure between these two kinds of 
underground organs, both of which often grow out as lateral buds from the 
same axis at the same node, and apparently under the same conditions. 
The main difference in structure, apart from the great increase in paren- 
Text-fig. 9. Transverse section of a bundle from 
a normal tuber of E. arvense. x 275. 
