268 
THE GARDENING WORLD 
March 28, 190 
than Nature herself possesses, but it is owing to Nature’s 
adaptability that the opportunity is practicable after all. A 
sidelight is thrown on Nature’s leanings by the fact that, 
broadly speaking, the plants from the' East do not readily, if at 
all, hybridise with species of the same genus from the West. 
Ages of growth under different conditions have probably caused 
a greater functional divergence between eastern and western 
By courtesy of Messrs. Webb andjSom. 
New Imperial Centaurea forms a very vigorous variety of 
Sweet Sultan. Very prolific in blossoms, which are of some size, of 
agreeable odour, and lasting when cut. (Seepage 273.) 
species than even that existing between so-called genera grow¬ 
ing in the same hemisphere. Hybridism is in a sense like elec¬ 
tricity ; we know not precisely what it is; all we know is what 
it usually does. 
One of the constants of Nature is variation, under varied 
conditions ; and one of the axioms of the cultural hybridist and 
cross-breeder is the fact that Nature seems to break her own 
laws now and then. No doubt Darwin saw this clearly when 
he formulated his broad aphorism or rule : “ Nature abhors 
perpetual self-fertilisation,” and we have illustrations of seem¬ 
ingly impossible hybrids appearing now and then only, in 
garden and field alike. Because a man has tried twenty times 
to obtain some particular hybrid and failed every time', it by 
no means follows that it may not occur under other and 
apparently very slightly different conditions with some other 
operator. In a word, Nature is like Mrs. Harriet Beecher 
Stowe’s Eliza, 'the loving mother in “ Uncle Tom’s Cabin ”; 
she tlmows nice rosy Apples', as ideas and expectations, along 
the ice of modern progress, and we hybridists are the children 
who follow them. 
If by this time our genial and indulgent Editor and his 
readers are not quite exhausted, I hope in my next paper, to 
allyde to the plants as inventors and producers, not in nature 
only, but in cur wide world of gardens and gardening as well. 
Since I began these letters or articles 1 have had expressions 
of opinion about, them from many sources. Some praise, others 
blame; some sneer anonymously, others laugh and joke, and 
sign their names ! I am grateful for any advice or caution, 
or intelligent hints and warning that any brother gardener cares 
to give me, but I shall, all the same, “ read, mark, learn, and 
inwardly digest ” this correspondence, and follow the oldest of 
advice of any we know, viz., to “ do my best, and trust that 
whatever follows is for the best ” of everyone who cultivates 
a garden, be it large or small. 
Something about Plant Food. 
(Continued from page 181.) 
Bt J. J. Willis, Harpenden, Herts. 
To the untrained mind, the perusal of a. statement of a soil 
analysis conveys no tangible idea of the amount of the con¬ 
stituents' declared therein, and contained in any definite depth 
of soil ; say, for instance, 1 acre of land. An approximate idea, 
of the weight of soil gives a relative idea as to its richness, or 
deficiency, in any of the mammal ingredients. 
One acre contains 43,560 square ft. of surface, and a depth of 
1 ft. of that aa-ea, therefore, contains 43,560 cubic ft. of soil. 
The weight of 1 cubic ft. of soil varies' greatly from the heaviest 
— that is, the rocky and sandy soils.—to the lightest—the 
peaty, loamy, and clayey soils. An average garden soil will 
weigh about 80 lb. per cubic ft., sc. that the weight of 1 acre of 
diy soil 1 ft. deep would be about 34 million lb. This being 
so, a soil containing 1 per cent, of potash or phosphoric acid 
would contain 35,000 lb. of such plant-food on an acre 1 ft. 
deep j or, again, should analysis, disclose one-tenth of 1 per 
cent,, the amount on that area would be 3,500 lb. ; and a crop 
removing, say, 50 lb. of potash, phosphoric acid or nitrogen a 
year would thus take 700 years, or, in the other case, seventy 
years to exhaust such a. soil absolutely of either of the sub¬ 
stances mentioned. 
Although, theoretically, that lapse of time would be neces¬ 
sary for the crops to entirely exhaust that soil of its potash, or 
some of the phosphates and nitrogen, it is nevertheless found 
in actual practice that beyond a certain limit the soil tena¬ 
ciously holds up and refuses to. part, with its store of plant-food 
in favour of the growing crop. It thus becomes necessary to 
restore to the ground those elements of plant-food which have 
been removed if successful culture is to be maintained. 
It is, however, fortunate that the future is thus protected 
against the rapacity of the present. 
These facts teach us the important lesson that it is not the 
total proportion of nitrogen, of potash, or of phosphoric acid 
that rules the soil’s fertility for horticultural purposes, but 
rather the amount of each of them that is present in an imme¬ 
diately available form. 
AVAILABLE PLANT-FOOD. 
This question of the availability of plant-food in soils has 
been dealt with more or less fully during recent years, and has 
attracted special attention at the Rothamsted Experimental 
Station. 
For example, in one of the experimental fields which has 
grown wheat every year since 1844 up to. the present time, a 
period of sixty years, both without manure, and with different 
