THE MONTHLY BULLETIN. 467 



WEED DISSEMINATION. 



By O. W. Newman. 



"The problem of weed destruction is perennial in every land where 

 agriculture is practiced. Indeed, so serious is it, that soil culture may 

 be said to be an everlasting war against weeds. For a thorough under- 

 standing of the weed problem it is necessary not only to define a weed, 

 and to study its relation to crops, but to ascertain what are the agents, 

 natural or artificial, which act as weed destroyers." 



The above statement is the opening paragraph of a very interesting 

 article by Dr. Silvester D. Judd on "Birds as Weed Destroyers," pub- 

 lished as a reprint from the United States Department of Agriculture 

 Yearbook for 1898. Having given the definition of a weed and its 

 relation to crops in a previous article, the purpose of the present paper 

 is to point out how weeds are disseminated and thereafter give some of 

 the agents which act as weed destroyers. 



I have enumerated seventeen different w^ays in which plants succeed in 

 scattering or disseminating their kind. Roughly they may be grouped 

 under four heads : 



1. Physical forces : wind, water. 



2. Mechanical devices : explosive pods, hygroscopic movement. 



3. Vegetative reproduction : root stock, serial stems. 



4. Animals : man, furred animals, birds. 



It is apparent that not all the seeds which a plant produces germi- 

 nate. If they did it would be impossible to prevent them from covering 

 the earth like a mat. However, Dame Nature has planned things so 

 nicely that each living thing — be it animal or plant — has some check 

 upon it, and it has been only by continued selection of the fittest to 

 survive that all the various forms of life, as we have them today, are 

 present. This struggle for existence has caused plants to seek the lines 

 of least resistance, and conditions of life have made one or the other of 

 these methods of dissemination the best. Certain plants which live in 

 more or less warm, dry, open places discovered that the wind was the 

 best means of spreading their seed. Hence they developed wings, like 

 the maple ; parachutes, like the milkweed, dandelion, etc. ; or a round, 

 ball-like form, such as the Russian thistle or tumbleweed. Other plants, 

 living in moist places, discovered it was better to develop air chambers 

 in the seed coat, like the lace-pod or sedge, or a corky covering such as 

 v/e find in dock, so that the least flow of water would carry them to 

 foreign parts. 



It is important to know which weeds are carried by the wind and 

 which by water. If you are called upon to eradicate Russian thistle, 

 tumble mustard or any of the true thistles — all of which are spread by 

 the wind — from a given territory, removing them from that piece of 

 land is only a check, not eradication. The source of infection must be 

 found and measures taken to prevent a second infestation. The problem 

 with regard to these weeds is exactly the same as with the red spider 

 and other pests spread by the wind. 



It is necessary to use entirely different methods of eradication for 

 weeds spread by water. Mr. "Waite, county commissioner of Imperial 

 County, has been experimenting with devices to prevent the spread of 



