193 
OBSERVATIONS ON THE PECULIAR GROWTH 
HABIT AND THE ANATOMY OF DOG’S MERCURY 
(MERCURIALIS PERENNIS L.)- 
N. GILL. 
Introduction. 
In the majority of English herbaceous dictoyledons the 
growing point of the aerial shoot gives rise, in succession, to 
the following structures : — • 
(1) Leaves with axillary vegetative buds. 
(2) Leaves with axillary inflorescences. 
(3) Bracts with axillary flowers. 
In some species the final stage is the production of flowers 
without the subtending bracts. According to Warming 1 this 
is the result of a tendency in the vegetative axis, to the earlier 
production of the flower at the expense of the bract, so that, 
finally, the flower only may be produced. In many species 
the production of axillary inflorescences does not occur and 
the growing point reverts directly from formation of leaves 
with axillary vegetative buds to the production of bracts with 
axillary flowers. In each case, however, the aerial shoot 
tends to terminate in an inflorescence and the apical meristem 
either becomes transformed into a terminal flower of the 
inflorescence, or is represented at the apex of the inflorescence 
as a small mass of tissue no longer meristematic. Thus after 
production of a terminal inflorescence, all elongation growth 
of the primary axis is, of necessity, brought to a close, and if 
elongation growth is to continue it must be carried on by 
development of shoots from the lateral buds below the 
flowering region. 
A few exceptions to the general growth habit outlined 
above occur in England, the most common being Mercurialis 
perennis L., which has therefore been examined in some 
detail during a study of the effect of flower production upon 
the anatomy of the plant axis. 
The Growth Habit of Mercurialis perennis L. 
This is one of the earliest English flowering plants, appear- 
ing in full bloom about the end of February. Mercurialis 
perennis is peculiar in that it produces the following suc- 
cession of structures upon its primary axis : — 
(1) Leaves with axillary vegetative buds. 
(2) Leaves with axillary inflorescences. 
(3) More leaves, and not bracts with axillary flowers 
as in the system described on page 195 (fig. ia). Very few 
1 933 Sept. 1 1 
