THE TROPICAL AGRICULTURIST. [August i, i«y3. 
MOISTURE OF THE SOIL AND ITS EFFECT 
ON PLANT LIFE. 
It in BometiineB extremely instructive to compare 
general results derived from study of living plants 
in the field vpith special conclusions obtained by 
experience in the laboratory. As a general rule the 
last method of inquiry leads into a wilderness of 
conflicting and contradictory statements, especially 
when the experiments have been conducted by 
independent observers ; of course, a single set of 
experiments conducted by one person is (if it give 
any conclusion at all), more or less harmonious. 
Still, when one does find any double confirmation 
of this kind, the result is probably more valuable 
than any reasoning from either method alone ; and 
in tlie following few facts, I have found such a 
double confirmation. 
A series of very excellent papers has recently been 
published in Germany on the different capacities for 
retaining and conducting water shown by different 
soils, and these explain certain peculiar phenomena 
in plant life. 
Thus, if one arranges a series of soils such as, 
sand of a quartzose character, loam, leaf-mould w"ith 
a certain amount of lime and sand, pure leaf- 
mould, clay and peat, these will be found to vary 
as follows: - 
The thicker or denser soils will be able to retain 
a larger amount of water than the loose and sandy 
ones, and this result holds true (Prof. WoUny, 
Fornchniit/eii, vol. v., p. I) in the same kind of soil 
if the particles are closer together in one case than 
in the other. For instance, beating the soil in a 
pot, and pressiui; it closely down, makes it able to 
hold more water than if the earth is lightly poured 
in. The reason, oi course, is, that the particles are 
so close to one another, that they form narrow 
capillary passages which retain the water in the 
same wuy as ordinary capillary tubes. 
For a similar reason these thicker clayey soils 
do not thaw so quickly as the loose sandy ones, and 
in long-continued drought, the cracks formed by the 
sun are fewer in number (though deeper and nar- 
rower) than those produced in the looser sandy 
ground ; in fact, all changes in temperature are felt 
more rapidly and severely in loose sandy soil than 
they are in thick clay or loam, which becomes more 
slowly heated and cooled, though retaining the heat 
for a longer period. 
This explains a point which always greatly puzzled 
me in Egypt. Between Cairo and the Pyramids 
there is a stretch of fiat ground, mostly pure 
alluvial of the Delta, but turning into the ordinary 
desert sand, about half to a quarter of a mile before 
the low limestone hills on which the Pyramids are 
built. (Part of this forms the links of the Mena 
House Hotel.) 
1 noticed that when the soil was even very slightly 
clayey or alluvial, many small herbaceous plants and 
a few perennials grew upon it ; but when there 
was no sign of alluvial, scarcely a single plant grew 
there, and the few which did exist, were all the 
regular desert forms which seem to subsist chiefly 
upon dew. The line was so well marked that one 
could almost have drawn it upon the soil, and in 
view of the preceding experiments, the reason is 
quite obvious. These little herbaceous Thistles and 
Plantains could not live unless the soil retained a 
certain amount of water for them, and it waa -.».y 
the fine-grained alluvial particles which were able 
to do this. 
Another point brought out Professor WoUny and 
Herr Bser in the same Jouimil, vols. vi. and vii., 
is the effect of plants on the temperature of the soil. 
Thus it was found, that ground which was covered 
by plants did not become either so hot in summer 
or so cold in winter as that which was left exposed, 
and tlie daily change in temperature was also mncb 
less than i < bare ground. It was also found th&t 
ground covered with straw or manure was not so well 
protected against these changes as that covered with 
living grass, and that the closer and thicker the 
stems of grass or corn were planted, the better was 
the protection against changes of temperature. It 
seems probable, from other experiiuenls, tliat these 
differences are due to the way in which evaporation 
from the soil is checked by living plants. '1 he 
plant-covering acts as a sponge, and after a shower 
of rain retains a large amount of water, which is 
only given off gradually afterwards. This explains the 
familiar fact, that the disappearance of forests osually 
produces drou(;ht in hot climates, as instanced by 
the Cape de A'erde Inlands, which, when discovered 
by the Portuguese, were covered with forest and 
very fertile, and are now exceedingly barren and 
arid, and only possess a single tree. This probably, 
also in part explains why ponds which are sheltered 
ay trees do not freeze so quickly as those which are 
exposed — for instance, St. J auies s Park, as compared 
with the Round Pond. 
There is also a peculiar reaction of surroundings 
on plants, and plants on tbeic surroundings in this 
connection. A tropical forest, where there is great 
humidity of the air, is always extraordinarily full 
of plants and exceedingly dense. The trees are very 
close together, and there is au enormous amount of 
undergrowth, wliile the creepers fill up every avail- 
able space between the undergrowth and the upper 
branches. This extreme density of the foliage ie 
not nearly- so marked on the tops of mountains, 
and sometimes disappear altogether on the crest of 
a mountain or a plateau, where the wind can sweep 
the moisture away. One sees exactly the same thing 
in this country ; any very narrow valley or glen 
among the hills is, when left alone, much more 
crowded with vegetation than an exposed wood, and 
grass grows much more closely on stifl or wet ground 
than it does on light and loose soils. 
One might multiply conclusions and hints of this 
kind indefinilely, but perbap i enough has been said 
to show the value of such laboratory cxLerimeuts, 
which seem unfortuuately to be made only in Ger- 
many, and not to have found au abiding place iu 
our own country, where agriculture certainly re- 
quires the best scientific assistance. — G. F. bcoTi 
Elliott. — Gardeners' Chrottidf. 
HARDINESS OF EL'CALYPTLS GLOBULUS 
AND E. COCCIFERA. 
A note appeared in one of the New York garden- 
ing publications recently, setting forth the failure of 
a test for hardihood with eeedlings of Eucalyptus 
globulus and E coccifera. As these trees grow so 
rapidly, and are so very distinct in character, I 
think tliey are worth planting in the south of England; 
even though they get frozen e\ery few years (say 
eight or ten), but they will attain a large size in 
that period of time. The experiments at Kew should 
be repeated with the supposed hardy types. I have 
not been in communication with the Gardens since 
the retirement of Sir Joseph Hooker, but perhaps 
some one there will see this note in your columns, 
and pardon me for any seeming want of courtesy. 
Kew is not Tasmania, and I do not see how it 
could be expected that j-oung soft seedlings would 
survive an English winter. Unripened Eucalyptus 
wood will not endure 1° of frost. Young trees of 
12 or 14 feet high are often killed back for 3 leet or 
more, with the thermometer barely touching .32° 
Pahr., when they are growing in swampy places. 
On hill sides they often escape, simply because there 
is less frost, and the wood is better ripened. It is 
well known that woody trees will stand considerable 
frost. I have had one out here which stood 22° 
Fahr. I then took it in, and wintered it out of pure 
pity, although I had to cut oil 5 or 6 feet to house 
it. Try again, and keep the young plants in pots until 
they are strong and woody.— James MacPheeson, 
Tasmania. — Gardeners' Chronicle. 
