PARK AND CEMETERY. 
moved in spring, never in autumn, just 
as is the case with magnolias. 
The other illustration. Yucca glauca, 
is the species usually catalogued un- 
der the name of Y. angustifolia. It 
has much to recommend it. Hardi- 
ness, to start with, it has, coming as 
it does from Colorado. Then there 
are its thread-like, narrow leaves, 
which its name angustifolia implies. 
And as the plant gets of some age, as 
the one photographed had, there arc 
at times two dozen spikes of flowers 
on it, all expanding at once. This 
yucca is the lirst to flower in spring. 
It and filamentosa are the two found 
in collection here, and glauca leads 
the other in flowering by fully ten 
days. When first introduced east 
from Colorado it was considered as 
an acaulescent species, but it makes 
stems, not as rapidly as gloriosa — 
which also is hardy here — but it does 
FLOWERS OF LIRIODENDRON 
TULIPIPERA. 
make them, the one of our picture 
having them nearly a foot in length ; 
and where wild they are found elevat- 
ing the tops several feet at times. 
The prominence of forestry matters 
has brought the catalpas to the front 
pi eminently of late. For hardiness 
and tree-like growth the speciosa is 
the better one, but when flowers are 
the object, plant bignonioides where 
it is hardy. Its growth is more 
spreading, giving to beholders a view 
of its panicles of beautiful flowers; 
and a large tree of it in full flower, 
such as are not uncommon in the mid- 
dle states, is a sight those who see it 
for the first time never forget. 
Pterostyrax hispidum is one of the 
grandest small sized trees we have. 
Later on many a person will regret 
not having planted one years ago. 
Joseph Meehan. 
SAP AND ITS INFLUENCE ON THE CARE OF TREES 
Within the last few years the prob- 
lem of the ascent of water in trees 
has entered on a new stage of exist- 
ence. The researches which have led 
to this new development are of such 
weight and extent as to establish a 
new and indisputable method that 
makes the former methods that have 
been taught incorrect, and therefore 
of little value, except as ancient his- 
tory. The two questions to be con- 
sidered are; (1) What is the path 
of ascending water? (2) What are 
the forces which produce the rise? 
The question has gone through va- 
rious theories (all admirably sum- 
marized in Ward's ‘'Timber and Some 
of Its Diseases”). The change in bot- 
anical speculation began with those nat- 
uralists who, concluding that no purely 
physical cause could account for the 
facts involved the help of the living 
elements in the wmod. To Godlewski 
is due the credit of this notable theory, 
still held by some students. 
What is regarded as the newest and 
most widely accepted theory, how- 
ever, is that of Dixon and Joly, which 
is based upon a pow'er of water in 
thin threads to resist tensile stress, 
combined with the fact that a trac- 
tional force is exerted on the water 
columns by evaporation from the leaf 
under the energy of the sun’s rays. 
This theory of sap ascent, elaborated 
by Dixon and Joly, is fully given with 
descriptions of their experiments in 
the ‘‘Proceedings of the Royal Socie- 
ty," London, Vol. .57, and is reaffirmed 
in 1900 in "Nature," Vol. 62, published 
in London. The fact that transpira- 
tion is not only accelerated by direct 
sunshine, but even more influenced by 
warm dry winds, supports the view 
that the evolution of vapor at the leaj 
obeys the general laws ot evaporation 
from a moist surface, and that the 
inflow^ of thermal energy is developed 
through evaporation, the leaves being 
the principal agent, proved by care- 
ful experiments which have been 
made by the most scientific botanists 
of the world. The roots of a tree 
also absorb the water in the ground 
very rapidly, and the cause of the 
death of so many trees on our 
streets is from the want of the mois- 
ture that is needed to protect the life 
of the trees, and the development of 
its leaves and branches. Unless there 
is moisture enough to be drawn from 
the roots, the tree cannot possibly sup- 
port the leaves, or enable the wounds 
made in cutting off the branches to 
heal, and all trees that are overloaded 
with branches should be pruned so as 
to be balanced to the changed condi- 
tion, from lawn or forest grounds, to 
street locations, where the same mois- 
ture cannot be had that is needed to 
develop both the wood and leaves. 
There should always, therefore, be 
an open earth space left at the roots 
of a street tree. The defoliaging of 
the street trees by insect pests will 
most certainly destroy them, if they 
are not properly sprayed, and the 
limbs of the defoliated trees always 
first dying at the extreme ends, en- 
tails an amount of the most expensive 
and dangerous pruning in, to save the 
life of the tree. 
The theory that some parasite will 
come to aid in the destruction of 
these destroyers of our beauiful trees, 
is the most dangerous heresy possible, 
as the immediate destruction of these 
pests when they first appear, by 
spraying with arsenate of lead, will 
save an enormous extra expense en- 
tailed by adopting this parasite the- 
ory. Even when a parasite is found, 
the increase of the insect pests is so 
great that parasites cannot at present 
be produced in numbers enough to 
meet the enemy. 
In conclusion let me repeat that the 
best time to trim all fruit and decidu- 
ous trees is in the month of May, 
and up to the middle of June in all the 
western and northwestern states or 
after the leaves and blossoms are 
formed, and their sap drawing quality 
is at its best, to heal both bark and 
wood. An active experience in both 
orchard and street tree work for over 
thirty years, with careful experiments, 
has proved that no winter, autumn, or 
midsummer pruning should be done, 
if you wish to get the best results. 
1 am indebted to Annals of Botany, 
Vol. X, and to Prof. Ganong, of 
Smith college, in this matter of the 
ascent of sap, and the most exhaus- 
tive of experiments made in the lab- 
oratory and field by such able botan- 
ists as Dixon and Joly has proved this 
statement to be thoroughly scientific 
both in theory and practice. 
Christopher Clarke, 
City Forester, Northampton, Mas.s. 
