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Proceedings of the Royal Irish Academy. 
secondary ones super-, mid-, and infer- Arctic and agrarian zones re- 
spectively. Each of these zones is characterized by the presence and 
absence of certain species ; or, in other words, one set of plants find 
their upper limits in each zone and ascend no higher from below, 
while another set find their lower limits in the same zone, and descend 
no lower. Briefly, he characterizes the zones thus : — 
6. Super- Arctic zone, 
5. Mid- Arctic zone, . 
4. Infer-Arctic zone, . 
3. Super-agrarian zone, 
2. Mid-agrarian zone, 
1. Infer-agrarian zone, 
Salix herbacea, without Calluna. 
Calluna vulgaris, without Erica. 
Erica tetralis, without Pteris. 
Pteris aquilina, without Rhamnus. 
Rhamnus catharticus, without 
Clematis. 
Clematis, Ruhia, Cyperus longus. 
This formula will be found at page 492 of his fourth volume ; but 
a little farther on he gives a fuller series of illustrations of each zone. 
There the reader will find that the lower limit of the super- Arctic 
zone is evidenced by the cessation of six species which are all high 
Alpines that do not occur at all in Ireland. And also, in accordance 
with the test plants adduced above, it would appear that this zone 
does not exist in Ireland. IN'o mountains are high enough to escape 
from Calluna in Ireland, excepting, perhaps, a small space (300 feet) 
of the highest point of MacGillycuddy's Eeeks. Its absence there is, 
however, probably due to insufficient soil to nurture the roots, and 
stunted barren plants were found within a hundred feet of the summit. 
At that latitude, were circumstances favourable, Calluna would prob- 
ably range at least 3500 feet. 
Similarly, the lowest zone (infer-agrarian) is characterized by its 
holding within its bounds a certain group of plants which can ascend 
no higher. Of these, eight typical ones are quoted : three of these 
only occur in Ireland. In fact, this whole group contains about two 
hundred species (exclusive of Eubi) and hardly a tenth of these are 
native in Ireland. This zone is mainly represented in the south and 
south-east of England, as the uppermost one is in the north of Scot- 
land, and on the summits of its highest mountains. The plants of 
Ireland ought to fall, therefore, within Watson's four intermediate 
zones. The species dealt with in my table may be distributed amongst 
the mid-Arctic, infer- Arctic, and super-agrarian zones ; while the re- 
mainder of the Irish plants not there treated of should belong to the 
mid-agrarian. It will be found, however, that there are several 
