TRANSACTIONS OF THE SECTIONS. 99 
the soil is said to be generally retentive of moisture. Although the geology of the 
other provinces in the North of Spain is in some respects essentially different, there 
are good grounds for believing that their climate is similar to that of the Asturias. 
When we turn to the Asturian districts of Ireland, we find more features of geolo- 
gical and physical resemblance to the North of Spain than in any other districts of 
equal area in Iveland. The influence of climate, which seems of paramount impor- 
tance in relation to plants, is very remarkable in the Irish Asturian districts. The 
author illustrated his views by reference to a Map, on which were projected the iso- 
thermal lines of mean annual and mean winter temperature for Ireland. These lines 
were drawn by the aid of observations made at some new stations, in addition to 
those on which he had to rely when projecting the isothermals already published. 
Among these stations he especially referred to Galway, from its position in the West 
Asturian district. From the Map, it appears that the greater part of the areas of 
both of the Asturian districts lie between the annual isothermals of 52° and 51°, and 
between the winter isothermals of 45° and 44°. These are the lines of highest tem- 
perature in [reland, and the winter lines correspond almost identically with those 
belonging to the middle of the province of Asturias itself. On the other hand, the 
summer temperature of the Irish Asturian districts is from 57°5 to 59°38 respec- 
tively, and therefore from 6° to 8° lower than that of the North of Spain ; whence 
it follows that if plants were introduced into an Asturian district from Spain, 
some of which required a warm summer, while others required only a mild winter, 
the former would die, while the latter might survive, and even spread over exten- 
sive areas. The condition of great summer warmth seems to be especially required 
for annuals belonging to southern climes, as the ripening of the seeds would be in- 
evitably checked by a single cold and wet summer. The growth of perennials ap- 
pears to depend principally on the condition of winter temperature, as these plants 
may spread by roots and suckers. After referring to the generally admitted fact 
of the moisture of the climate of Ireland, the author concludes, from observations 
made at Galway, Innishgort, in Clew Bay, and Lough Corrib, that the annual rain- 
fall in the West Asturian district must at least exceed 50 inches; while observa- 
tions made at Valentia, Killarney, Cahirciveen, and Castletownsend show that the 
fall is probably still greater in the South-west district. 
Corresponding conditions exist with regard to the relative humidity of the air. 
Tf, as before supposed, different varieties of plants from a southern clime were by 
accident introduced into our Asturian districts, for some of which moisture was 
more favourable than to others, the former would have a far greater chance of be- 
coming widely spread, while the growth of the latter might be checked instead of 
being promoted. 
The influence of cultivation in promoting or checking the introduction of wild 
plants into the Asturian districts was next discussed. It appears from returns fur- 
nished to the Registrar-General of Ireland during five years, that the greatest pro- 
portion of weedy ground was observed in the Asturian districts; and from returns 
made during several years of the relative areas under tillage, pasturage, and ina 
totally uncultivated condition, that the Asturian districts were the lowest in general 
cultivation among districts of equal extent. 
Although annuals and the class of weeds generally accompanying crops are at 
first fayoured by culture, which opens the soil for their propagation, it seems that 
the tranquil development of perennial wild plants takes place most completely 
where culture is imperfect or entirely suspended ; whence it follows that if any 
perennial wild plants suited by their habits to the Asturian district happened to be 
introduced into them, their chance of existing and spreading would be greater than 
in other districts of Ireland. In addition to the evidence furnished by the returns 
of the Registrar-General, the author referred to the writings of Arthur Young, and 
to the Agricultural Surveys of the counties of Ireland, in order to show that the 
same relative condition of the Asturian districts with reference to cultivation had 
been in existence as long as the subject had attracted any notice. It was shown by 
numerous references, that a great many well-authenticated instances of the intro- 
duction of plants through commercial and general intercourse have greatly changed 
the flora of different countries. These changes were often effected within a com- 
paratively short period of time, and they were more or less complete in proportion 
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