400 STATISTICS OF THE ORDER CRUCIFER”. 
tory of the plants of this Order that their number is on the m- 
crease among us. Several species have been added during the 
last few years to our lists of British plarits, and we are not aware 
that any of them has recently disappeared. 
These are the statistics of the Order, and they are precise and 
definite only in the species growing among us. Data are wanting 
for equally satisfactory statements in reference to the numbers 
and proportion of Crucifere in the general Flora of the globe. 
What is to be here advanced about the periodicity, duration, ha- 
bitats, and range of the species is to be understood as limited to 
British species, and to their accidents in Britain. 
We intend at some time or other to give a series of articles on 
these physiological aud geographical properties of plants in general 
which we express by the technical terms periodicity, duration, 
range, and habitat. By periodicity is to be understood the time — 
or period when a given plant is in flower, or when it perfects its 
seeds; duration implies the extent of time during which any 
given plant exists as a living being, or organism, as some would 
express it; habitat means the general habitation of the species, 
the situation on the soil, where it grows; and the range is its ex- 
tent over the earth’s surface, either horizontal or vertical. In all 
the four seasons, in every month of the year, even in our northern 
latitude, some at least, and often several, species of the Crucifere 
are to be found in flower. The Shepherd’s Purse is always in 
flower, and generally in fruit also, except when the soil has long 
been bound up by severe frost or covered by a thick coat of snow. 
Draba verna and D. aizoides appear in March usually, and in 
very mild seasons in February, or even in January: the former 
was noticed as early as the 3rd of January, in the year 1853; 
the latter is one of our most local plants. Cardamine pratensis is | 
rarely later than the end of March, and C. hirsuta or sylvatica, espe- 
cially in warm, sandy, sheltered places, is in flower almost a month 
earlier than her prettier sister, Our Lady’s Frock. C. amara is 
somewhat later than C. pratensis. This one may, in late seasons, 
be found in flower in June, but in the south of England May is 
the time when it may generally be found both in flower and in 
fruit. Sisymbrium thalianum is one of the early flowerers: it 
appears with Cardamine pratensis, not in the same place, but 
about the same time. The Wallflower is never later than April 
in gardens, and it is rarely found anywhere else; but the genuine 
