THE MEDITERRANEAN NATURALIST 
99 
highly hygrometric and absorb the dew, which they 
transfer into the interior of the plant. One of the 
best instances is Reaumuria hirtella , allied to Ta- 
marix , which also does the same to some degree. 
Reaumuria is a shrub growing sometimes to two 
01 three feet high. After rain and the leaves have 
been well washed, on the following morning the 
leaves are found to be covered with drops, the 
result apparently in this case of root-pressure. As 
the day advances, the leaves become dry and are 
then covered with a fine powder, consisting of salts 
of chloride of calcium and of magnesium. These 
are secreted by special glands in the epidermis. 
They act as absorbents when the rainy season is 
over, and the plants have to depend almost enti- 
rely upon the dew for their supply of moisture. 
The above constitute some of the more remarka- 
ble structures which enable desert plants to thrive 
in the most inhospitable region of the world. 
(To be continued.) 
Military Pigeons, 
Since the success of the carrier pigeon service 
during the siege of Paris in 1 870-“ 1 , European 
governments have given considerable attention 
to the rearing and training of pigeons. In Fr 
ce, according to Lieut. Col. De Rochas, most of 
the fortresses now contain dovecotes, and 47 
departments have private societies for pigeon 
training, the total number of trained pigeons in 
the country being about 100,000, and Paris alone 
having 8, 000 trained and 10,000 untrained 
pigeons. In Germany there are about 20 mili- 
tary pigeon stations, and in 1888 there were 78 
private societies with 52,240 carrier pigeons. 
In Italy there are dovecots at 23 military sta- 
tions. Spain has a very complete system of pi- 
geon service, dovecotes having been established 
at 18 stations, the greatest distance between any 
two designed to communicate directly being from 
Madrid to Malaga, 240 miles. In Portugal there 
are 14 stations, in Russia, 5 stations, that at 
Brest-Litowsk having 1000 pigeons; in Switzer- 
land, 4 stations; in Austria 2 stations and seve- 
ral projected ones; considerable government en- 
couragment being given also to private trainers. 
Sweden has one station; Denmark, a private 
society in 12 sections; Belgium, many private 
trainers, with an estimated total of more than 
600,000 pigeons. Holland has a regular pigeon 
postal service between Java and Sumatra; and 
England, a number of cotes in garrisoned cities. 
Theories of Mountain Formation. 
BY T. MeLLAED ReADE, C.E., F.G.S., F.E.l.B.A. 
Part III. 
In concluding the last article I promised to 
explain in what way the illustration given of the 
effects of expansion on various materials bears 
upon the origin of mountain ranges. 
But before doing this I must ask the reader to 
pardon a little digression, as I wish to call atten- 
tion to the discussion which took place at the 
Geological Section of the British Association on 
the 10th of September 1888 on Profesor E. W. 
Clay pole’s paper entitled a (1) “Note on Some 
Recent Investigations into the Condition of the 
Earth.” This paper dwelt with the discovery of a 
“level-of-no-strain” in a cooling globe already 
explained in the first article. 
It so happened that none of the men whose 
name are associated with this investigation -were 
present, and as I was admittedly fortunate enough 
to be the first to announce the discovery (2) it may 
not be inappropriate for me to correct some of the 
misconceptions that seemed to prevail among the 
disputants. Professor Claypole said — “Of the 
actual existence of such a zone, after a careful 
study of these investigations, scarcely a doubt can 
entertained,” but suggested that the numerical 
calculations of the depth at which it now lies 
might be in error, as we have many examples of 
rocks being “forced up from a depth greatly ex- 
ceeding this limit.” The speakers who followed 
mostly contended that such a neutral zone, where 
the cooling produces neither compression nor ex- 
tension, could have no existence, as there w r ere ex- 
amples in all quarters of the globe shelving that 
rocks had been squeezed, contorted, and forced up 
from much greater depths. The President most 
emphatically wound up the discussion by declaring 
his utter disbelief in the existence of a “ievel-of- 
no-strain” in our earth, having arrived at this con- 
viction through his geological experience, which 
( 1) Reported in Sclent pic A "a Sejtt. Ufth ISSS ■ 
(3) Origin of Mountain Range. s, chajihr XL. 
