436 SCIENCE PROGRESS 



upon light and air, so that they are unable to flourish satisfactorily 

 under the shadow of the crop even though all other conditions 

 of the soil, moisture, etc., are suitably adapted to their well- 

 being. The complete absence of Matricaria on the heavy lands 

 of Somerset has already been mentioned. 



Charlock. — The various weeds known as Charlock are very 

 widespread and very dominant in many places. Quite a number 

 of the Cabbage tribe come under this heading but two of the 

 most prevalent are Brassica Sinapis ("Charlock" proper) and 

 Brassica alba ("Mustard Charlock" or "Wild Mustard"). Of 

 the two, Brassica Sinapis is the more widely spread and in a 

 greater or less degree is found upon every soil. Brassica alba 

 is more of a chalk-loving plant and seems to flourish well where 

 the soil is very chalky, though it is often found on sand and 

 also appears on the calcareous clays near Bath. In some 

 places, the change in the nature of the soil in different parts 

 of the same locality is indicated by the change in the relative 

 dominance of the two species. In the Dunstable district, where 

 Charlock abounds, the foot of the hills is composed of a heavy 

 chalk marl which is populated by Brassica Sinapis as the 

 dominant weed ; going up the slope of the hill the soil changes 

 to pure chalk and Brassica alba (Wild Mustard) gradually takes 

 the place of the true Charlock. In some parts of the Wiltshire 

 downs where a layer of " bake " occurs above the chalk B. sinapis 

 reappears, so that sometimes the variety of Brassica met with 

 affords an indication of the nature of the soil. 



Another curious feature of Charlock is the way in which it 

 grows up under certain circumstances. If a well or deep hole 

 be dug, Charlock frequently makes its appearance in the 

 upturned soil, even in districts where this weed is quite 

 infrequent. This is not always easy to account for. It is 

 probable that the seeds are already in the soil in such cases 

 but buried too deeply to germinate and that as soon as they 

 are brought to the surface they start into growth. It is well 

 known that certain seeds are able to lie dormant for extra- 

 ordinarily long periods, often retaining their vitality during 

 many years. 



Many attempts have been made to devise some efficient 

 means of eradicating Charlock and nowadays spraying is the 

 method most in vogue. Frequently solutions of copper sul- 

 phate have been used but with varying success, as so much 



