MANURES AND THEIR USES. 
217 
guanos, found in some of the islands of the West Indies, are by 
far the most valuable fertilisers, whether natural or artificial, 
which have ever been offered to the public. Voelcker recom- 
mends them especially for Potatos and root crops. 
Texas guano is the pure excrement of large numbers of bats, 
deposited in certain caves near the coast. Dr. Voelcker says 
that Texas guano contains nitrogen in three distinct forms, viz. 
as organic matter, as ammonia salts, and in the form of nitrates. 
The two latter sources of nitrogen are readily available plant- 
foods, while the organic matter requires time for its decomposi- 
tion ; therefore it must form a reserve, or latent supply which 
becomes active after a time. 
Guanos, owing to their high price, are, and have been, greatly 
adulterated. The substances used for adulterating are sand, clay, 
gypsum, salt, powdered brick, and limestone. Sometimes Peruvian 
guanos are adulterated with cheap mineral phosphates in a finely 
ground state. Such phosphates have not the same horticultural 
or money value as the phosphates contained in genuine Peruvian 
guanos. The cultivator should, before he purchases guano, have 
a written guarantee stating the percentage of nitrogen and 
calcium phosphate present, and if any doubt is entertained of the 
genuineness of the manure it should be sent to an analytical 
chemist for analysis. 
Lime. 
Lime is one of the most widely diffused substances in nature, 
existing in chalk, limestone, marble, marl, calcareous spar, 
organic remains, &c. The bones of all vertebrate animals are 
composed chiefly of phosphate of lime. It is also found in the 
shells of beetles, crabs, lobsters, oysters, &c. Lime forms a large 
percentage of the weight of the ashes of plants, and therefore 
it is a very necessary plant-food. 
All crops do not contain lime in the same proportion, and the 
quantities are not constant even in the same plant. 
Lime is obtained by exposing pure limestone or chalk to a 
red-heat, the product being stone-lime, quicklime, burned lime, 
and caustic lime. Sometimes it is obtained by burning oyster- 
shells, or shells of other fish, converting them into quicklime 
termed " shell-lime." 
Lime has been used as far back as the time of the Romans 
for manuring fruit trees, for which it is most important. 
