194 Peculiar Growth Habit and the Anatomy of Dog’s Mercury. 
English herbaceous species recommence vegetative growth 
at the apex after the formation of flowers, and the only 
other species of which the writer is aware are Lysimachia 
thyrsiflora L., Lysimachia Numularia L., and Veronica 
Scutellata L. 
In Mercurialis perennis the renewed vegetative growth at 
the apex after flowering continues for a short time only, and 
from mid-summer to the death of the shoot, about November, 
no further leaves are normally formed at the apex, although 
the meristem is apparently still healthy. 
The cessation of activity of the apical meristem in the 
production of leaves coincides with the time when the leaves 
of the trees overshadowing the plants have attained full size 
and the intensity of light is thus greatly reduced. It was 
thought that this might be the factor bringing about cessation 
of apical growth. Large numbers of plants growing in shady 
woods were compared with plants growing in more exposed 
positions and it was found that normally there was no marked 
difference in the numbers of new leaves formed at the apices 
of the plants after flowering, the number varying, in each 
case, between one and five pairs. In some exceptional cases, 
however, plants receiving almost full daylight had apparently 
renewed terminal growth after the normal cessation of growth, 
and as many as five pairs of additional leaves formed above 
the normal ‘ post -flowering ’ leaves. These additional leaves 
were very noticeable, being of a light yellowish-green colour, 
in contrast with the dark green of the leaves below. The new 
growth stood out against the normal plants in the same way 
as the secondary elongation growth of oak and other trees 
referred to by Wight 2 and Dibb 3 . As a rule, only odd plants 
had developed as described, but in some well-exposed positions 
large numbers of such plants were observed. A careful search 
was made for similar plants in shaded positions, but without 
success. 
About the time of cessation of leaf production in normal 
plants, lateral underground buds at the base of the shoot begin 
to grow out to produce underground stems of varying length 
(fig. ib). At the apices of these the shoot of the following 
year begins to form. The young shoots reach an advanced 
stage of development before winter commences and the winter- 
rest begins after the leaves, together with the inflorescence 
initials in their axils, have developed. Thus, when renewed 
activity begins in spring the plant at first merely expands the 
leaves and floral organs formed during the previous summer, 
at the expense of food material stored in the underground 
stem, and after this expansion renewed growth of the apical 
meristem commences, giving rise to additional leaves without 
The Naturalist 
