532 ACCLIMATIZATION OF FOREIGN TREES AND PLANTS. 
There is no doubt we have a great deal to learn as to the 
mode in which plants propagate themselves in nature, which 
may be of the utmost value to our gardeners. Every one is 
familiar with the fact of the apparently spontaneous appear- 
ance in immense abundance, of plants in soil when subjected 
to certain farming operations, or on the sowing of some par- 
tieular crop. Whenever a new railway cutting or embank- 
ment is made, some ,plant unknown in the neighborhood is 
almost sure to appear, and either permanently establish itself 
or again disappear after a few years. The "sowing" of lan 
with lime is invariably followed by the appearance of a crop 
of white or Dutch clover. When certain kinds of wood are 
cut down it is said that during the next year a particular 
species of moss will always be found covering the ground. 
Immediately after the great fire of London in 1666, the 
London Rocket (Sisymbrium Irio) sprang up in enormous 
quantities on the dismantled walls, but is now no longer to 
be found in the metropolitan district. The usual theory to 
account for this sudden appearance of new plants is the 
existence in the soil of large " stores of seeds" ready to ger- 
minate on the first favorable opportunity. In his Anniver- 
sary Address to the Linnean Society in 1869, Mr. Bentham, 
however, pointed out that if this explanation was the true 
one, it ought not to depend merely on theory, but would be 
capable of easy practical verification. He suggested whether 
a hitherto insufficiently acknowledged part in the rapid dis- 
semination of plants may not be played by birds. The 
whole subject presents a wide field for farther investigation, 
and must amply reward any one who takes up the inquiry, 
if endowed with the qualities of accurate observation and 
patient research. 
Mr. Mongredien’s "Planter's Guide” deals chiefly with the 
introduction into this country of foreign trees and shrubs. 
Within the last twenty or thirty years the appearance of our 
lawns and plantations has been greatly changed by the num- 
ber of new forms which have made their appearance. The 
