Au ТРГ Ка eee IT 
hair on the upper surface 
· "соттоп 
THE 
Jury 24, 1875.] 
GARDENERS’ CHRONICLE. 
IOI 
THE B Pu сара OF THE 
ATO DISEA 
d Concluded from $. то. ea 
I Now give in conclusion an illustration of the per- 
fectly cube aa ities e of Peronospora infestans, 
as seen imbedded in the substance of the Potato leaf. 
These keting: sanis which carry on the winter life of 
the fungus, are not restricted to the leaves, for I find 
The engraving given herewith (fig. 19) shows a trans- 
verse section through a black spot of one of the leaves 
from Chiswick, and the resting-spore is seen at A nest- 
ling in amongst the cells of the leaf. An antheridium, B, 
and two oogonia (C, C), from which such resting-spores 
the same time, With care, however, they can be got 
at, when they will be seen, as at D, covered with 
brown-black and shining. They are spherical or 
slightly egg-shaped, and measure on an average about 
one-thousandth of an inch in diameter. I consider it 
T sss F 5 
exactly the same in size, conformation and colour with 
Peronospora arenariæ, Berk., an allied species found 
parasitic on Arenaria trinervis, In looking for these 
bodies care must be taken not to confound them with 
corroded cells the disease, 
or ur d: bodies 
E is shown a semi-mature resting-spore with 
Fic, 19.—THE RESTING-SPORE oft THE POTATO FUNGUs (A) EMBEDDED AMONGST THE LEAF CELLS, 
Enlar, 
ed 250 diameters.) 
Semi-mature resting- spore (E); mature ditto (р). (Enlarged 400 diameters.) 
arise, may be seen in the cut, and the old common 
form of the fungus will be noticed breaking through a 
of the leaf, which is a very 
The situation of the resting- 
ed on the leaves by 
for, when m ature, th 
only a little larger in size than the leaf-cells. 
so intense brown-black in colour from 
as hard 
And then setting them free by crushing the s 
ееп two slips of glass. The presence of the 
fungus in the leaf makes the cells very thick and 
р. te as well as black, so that in crushing the leaf 
n the resting. 
spore is not uncommonly crushed at 
pollinodium attached, РЕНЕ half washed out of 
its coating of cellulose by maceration in water. 
I may say as an addendum that to me there is a 
the other hand between the simple-sp 
antheridia. I consider that the oogonia and an 
are merely the i condition of the swarm- 
spores and 
of the former. 
The facts which point in 
are these :—Sometimes there is no differentiation in 
the contents of the swarm-spores, but the plasma is 
discharged in one mass and not in the re con- 
dition, the swarm-spore DEN resembles the oogonium. 
At other times the oogon distinct diffe 
tiation in its contents, int pid 
ures from one to three 
“spores, which to me wide wi approach to 
penis at on of the swarm-spore. Worthington G. 
Smith, Milemay Grove. 
which latter are the aérial state | 
ELEMENTARY LESSONS IN 
BOTANICAL GEOGRAPHY. 
(Continued from p. 621, Vol. III., n.s.) 
X.—ON THE INFLUENCE OF MAN ON PLANT- 
THE influence of man in modifying the distribution 
of plants has been very great, and the den 
ben are soon pe in a tract of country w 
, the 
n the soil in 
uals. I will say a few words about each of 
these groups, illustrating them principally by referring 
to the flora of our own country. 
The plants which are specially liable to be destroyed 
in a tract of country fully occupied by man, are those 
that grow upon heaths and in woods and swamps. In 
Britain a large proportion of the whole surface is now 
turned into arable land, and there are whole counties 
i of 
gregarious, it is very unlikely that a species should get 
r knowledge of the botany of 
e very few plants which we 
grown wild in the island 
that € = Pasce at the present time, though 
some, 1 ypripedium Calceolus, Phyllodoce taxi- 
folia, at urens, and Asplenium germanicum, are 
either quite extinct or кашы оп жеры m verge of 
tak ct like 
they ssa that = -— species once kno 
list of w n that work at pp. 345- E 
are now чт to the жым = фес county. 
ions world, where the general 
plan of plant distribution is t, the 
duced e intervention of man is often far T 
Tn the tropics shade is an essential condition of life for 
a large proportion of the species, and when the forests 
are cut down these are killed. In the warm temperate 
zone the species are Бу ит more restricted in 
their range than in our north temperate latitudes, I 
ive an accoun i h Africa 
almost in the words of i 
upon the spot the botany of the colony. 
At the Cape the great grazing di ict is what is 
called the ии а tract which extends from the 
high Snewbergen Mountains north-eastward in the 
direction of Natal, and includes the provinces of 
and Albert. At the time of the 
luxuriant 
trees, ng its watercourses ^ ous 
Willow and eda ii luxuriated. This has been the 
ptis con ago eu of the Cape, but isnow 
being comely dix in the general character of 
its vegetation by o . When fist introduced, 
the s 
to give way. Sh d 
int ы he cult nd climate combined. mat Hors) 
was prominent, the shrubs 
aad as long as the grass was 
