2 COMMON WEEDS 



writing, indeed, some self-sown oats are flourishing in 

 full ear in the writer's garden, but on account of their 

 beauty are left among the flowers in a small group. 



i . Uses of Weeds 



Weeds are in general regarded as harmful, and in 

 future chapters will be so considered. It will be well, 

 however, to point out certain ways in which weeds may 

 be said to be useful. 



(a) Weeds may sometimes be the means of retaining 

 nitrates in the soil, especially in cases where the soil is 

 left without a crop for a time, as in bare fallowing. 

 Without the intervention of weeds nitrates may be 

 washed out. It is probable that other plant foods are 

 also similarly retained by weeds, and after these are 

 ploughed under the valuable constituents in them are 

 utilised by the next cultivated crop. As we shall see 

 later, weeds take up considerable amounts of the 

 essential plant foods. The growth of a green crop, 

 however, will have the same effect, and is doubtless 

 more useful than weeds, for, unless great care is exer- 

 cised, many of the latter will seed before being ploughed 

 under and ultimately cause trouble ; nothing is more 

 true than the adage, " One year's seeding is seven years' 

 weeding." 



(b) Another way in which weeds are useful annual 

 ones, perhaps, especially is that they act in the same 

 way as green manure when ploughed under, and even 

 such weeds hoed up and left to die on the surface 

 sooner or later become mixed with the soil and im- 

 prove it in various ways. During their active growth 

 they take up carbonic acid gas from the atmosphere, 

 utilise the carbon, and return the oxygen both acts 

 in themselves useful in purifying the air and, on 



