352 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
The Season and Length of Period of Growth, 
This is the last of what we have termed the governing factors, 
and has a very marked bearing on the question. Everybody knows 
that in the warm spring weather plant growth is more vigorous than 
at any other time of the year, but, like so many other factors in nature, 
we are accustomed to take it for granted without ever asking why. 
In order properly to understand the reason of the rapid spring- 
growth, it is necessary to have some knowledge of the action of soil 
bacteria. It is impossible in the scope of this lecture to deal with 
this fascinating study, but those interested should read the Masters 
Memorial Lectures given by Dr. Russell, and published in the Journal 
of the Society, vol. xli. pp. 173, 188. It is sufficient for our purpose 
to say that these minute organisms render available for the plant the 
food materials present in the soil and those we add to it in the form 
of manures, and at the season of the year when all life, both above 
and below ground, is waking from its winter sleep, the bacteria are 
at the height of their activity. Their work is briefly to break 
down the complicated compounds of ammonia, &c, and present them 
to the plant in a form in which it can take them up and feed on them. 
It is obvious therefore that spring- and summer-planted crops will 
not require such special attention in the matter of manuring as those 
that have to go through the winter, when the bacteria are dormant 
and therefore not preparing fresh food for them. 
No better instance could be given of this than spring-cabbage f 
which is planted in September to be ready for use in the early spring. 
The practical grower dresses his land well before planting out his 
cabbage, and thus provides food for them through the winter. Among 
agricultural crops wheat is a good example, and requires more manuring 
in available nitrogen, either in the form of dung or the remains of 
clover, stubble, &c, than is the case with the later-planted oats or 
barley. 
Every farmer knows that in a cold spring his wheat is apt to turn 
yellow ; this is because the low temperature checks the activity of 
the bacteria, and consequently the plant becomes temporarily nitrate- 
starved. To remedy the defect he will give a light dressing of nitrate 
of soda or sulphate of ammonia. 
Similarly mangolds, beet, and parsnips require heavier manuring 
than turnips, because the latter are later-planted and therefore get 
fuller assistance from the bacteria. 
Closely allied with this question of season is the length of the period 
of growth of the crop. It is obvious that a crop that is long on the 
ground, like cabbage, winter beans, parsnips, &c, among garden crops, 
and wheat and mangolds among farm crops, will require more lasting 
manures than those that are on the ground for only a short time. 
These, then, are the four governing factors which it is imperative 
to consider carefully if anything approaching correct manuring is 
aimed at. 
