12 PLANT PROPAGATION 
drainage, to sow thinly to avoid overcrowding, to 
ventilate sufficient to carry away an excess of moisture, 
and to water carefully so that the compost is not kept 
continuously in a state of saturation. If an attack be 
observed in its early stages, the seedlings should be 
immediately replanted in fresh compost, and the old soil 
and the affected seedlings burned to prevent the spores 
of the fungus from spreading. 
Seedlings do not always come true, but show varia- 
tions of character. In some cases of varieties that have 
been in cultivation for a number of years, if two of the 
same genus are grown in close proximity to each other, 
the resulting progeny from the seed will be considerably 
changed. Especially is this frequently the case with 
many of the Brassica family. For this reason seedsmen 
desirous of keeping their strains of choice sorts true 
have them* grown far apart in isolated localities, to 
prevent bees and other insects from conveying the pollen 
from one to the other, and thus, as far as possible, 
preventing cross-fertilisation. Another practice with 
them is to go over the ground, ‘‘ rogueing ” the crops— 
that is, pulling out and destroying any plants that do 
not exhibit the normal character, such as rampant 
growers instead of dwarf, compact examples, or, in the 
case of flowers, destroying before they seed any that do 
not come up to the standard of excellence desired either 
in colour or in habit of growth. 
For the production of fruit and fertile seed, fertilisa- 
tion of the flowers is needful. This is in some cases 
effected by the distribution of pollen by wind or insect 
agency. Artificial pollination with the aid of a camel- 
hair brush or by other means is sometimes desirable. 
In the case of species where the sexes are in different 
