CURRANT PESTS—CYTOLOGY 
“Red Spider” 
Tetranychus species 
In dry years great injury is occasionally 
done in plantations of currants and goose- 
berries, as well as on raspberries, apples 
and many other kinds of fruits, by vari- 
ous species of spinning mites which are 
usually spoken of in a general way, by 
horticulturists, under the name of “Red 
Spiders.” These are all very minute red- 
dish, or greenish white, mites that are 
found on the lower surfaces of the leaves, 
which they cover with a fine network of 
web in which they live and which ren- 
ders it difficult to get at them with or- 
dinary liquid applications. These minute 
creatures propagate very rapidly, and 
their injury to trees by sucking out the 
juice of the leaves is very soon apparent 
by the bleached appearance of the foli- 
age, which soon dries up and falls away. 
Remedy 
It is probable that most of the kinds of 
“Red Spiders” pass the winter as eggs on 
the bushes. Plantations which have been 
infested one year, should be thoroughly 
sprayed early in spring with the lime and 
sulphur wash. Sulphur has a specially 
fatal effect upon all kinds of mites. If 
bushes are found to be infested in spring 
or summer time, they should be sprayed 
forcibly with kerosene emulsion, which 
might be followed in persistent attacks, 
which often occur, by dusting the bushes 
while wet with powdered sulphur by 
means of one of the so-called insect guns 
or horticultural bellows. 
JAMES FLETCHER, 
Ottawa, Can. 
Scurry Bark Louse. See under Apple 
Pests. 
YELLOW CURRANT Fy. 
Maggot. this section. 
Cytology 
Cytology is the science which deals 
with the structure, development, and 
functions of the cell; of the multiplication 
of cells into organs and tissues. The cell 
has been defined as “A mass of pro- 
toplasm with a nucleus in it.” 
History of Cell Theory 
Cells were first discovered in various 
vegetable tissue, by Robert Hooke, in 
See Currant 
877 
1665, but it was not until the beginning 
of the nineteenth century that any insight 
into the real nature of the cell and its 
functions was obtained. In 1846, Hugo von 
Mohl was the first to recognize that the 
essential vital constituent of the plant 
cell is a slimy protoplasmic mass, in- 
side of the cell and not the cell itself. 
This mass was called the nucleus, and was 
distinguished from the cell wall which is 
now supposed to be a protection to the 
vital part, rather than the vital part 
itself. 
The cell theory, in so far as it relates 
to plants, was established by Schleiden 
in 1838. He showed that all the organs 
of the plants are built up of cells, that 
the plant embryo originates from a single 
cell and that the physiological activities 
of the plant are dependent upon the in- 
dividual activities of these vital units. 
This conception of the plant as an ag- 
gregate or colony of independent vital 
units governing the nutrition, growth and 
reproduction of the whole, cannot, how- 
ever, be maintained. It is true that in 
the unicellular plants all the vital ac- 
tivities are performed by a single cell, 
but in the multicellular plants there is a 
more or less highly developed differentia- 
tion of physiological activity giving rise 
to different tissues, or groups of cells, 
each with a special function. The cell, 
in such a division of labor, cannot there- 
fore be regarded as an independent unit. 
It is an integral part of an independent 
organism and, as such, the exercise of its 
functions must be governed by the or- 
ganism as a whole. 
Size of Cells 
Prof. Charles Joseph Chamberlain, 
University of Chicago, says: 
“Most cells are too small to be seen 
with the naked eye, cells which are 
visible without the microscope being ex- 
ceptional rather than the rule. The egg 
of a bird consists of a single cell, as do 
the eggs of animals and plants. The larg- 
est plant cells are the internodal cells of 
the stonewort, Chara, which reach a 
length of two inches. The largest egg 
cell for any plant is that of the Zamia, 
a plant related to the sago palm; this 
