PERIODICITY IN VEGETATION. 135 
March and April, flowers in Aberdeenshire in April and May. 
The Menyanthes trifoliata is not more than a fortnight earlier 
with us than it is in Scotland; and it is probable that the mid- 
summer flowers are only a week later in the northern parts of 
the island, while the July and August flowers are as early in 
Scotland asin England. The temperature of the summer months 
in Scotland is about as high as in England; but the difference 
of temperature in England and Scotland during the spring 
months is very considerable. 
The term periodicity, when referred to plants, comprehends the 
beginning, the duration, and the termination of vegetable life ; 
also the times when plants flower, ripen, seed, etc. The ascent of 
the sap and the falling off of leaves in the more permanent forms 
of plants are also periodic phenomena. ‘The repose, or apparent 
repose of vegetable beings, as in winter, when all outward signs 
of vitality disappear, and the diurnal changes which some plants 
assume when their blossoms shut or open, and when their leaves 
are fully expanded or partially folded up, are all referable to the 
same causes. These causes are mostly beyond our ken; but we 
profess to deal with facts or results only, and some of these we 
have now laid before our readers. Another remark may not he 
impertinent. The terms annual, biennial, and perennial have 
been stated to be very indefinite; the first characterizing plants 
which live a few weeks, or which may prolong their lives for 
several years. ‘The second is applied to plants which, under 
ordinary circumstances, never flower till the year following that 
year in which they germinate, but which may exist five or six 
years. The third class embraces plants which live from two or 
three years to as many as twice two or three thousand years. It 
has been advanced that all plants may be classed by their dura- 
tion into two classes; viz., first, such as flower only once from 
the same root; and second, such as flower oftener than once 
from the same root. (We intend to devote an article to her- 
baceous, shrubby, ligneous, evergreen, and deciduous plants.) 
Our remark is this, and it will be shorter than our preamble: we 
do not quarrel with the words annual, biennial, and perennial, 
nor do we wish to supersede them, or even to see them superseded 
by more philosophical expressions. We merely wish to inform 
our readers, that these terms are not to be understood in their 
strictly literal or verbal sense: and further, our wish was to state 
their import as employed by botanical writers in general. 
