18 
Colorado Experiment Station 
Tlie factors wliich affect the imiiilier of weed seeds car- 
ried in irrigation ditches are as follows: 
1. Flora of ditch l)ank and adjacent territory. 
2. Season of the year. 
d. Velocity and direction of wind. 
4. Velocity of irrigation stream. 
5. Buoyancy of weed seeds. 
DITCH BANK VEGETATION 
In the construction of irrigation ditches, both large and 
small, new soil is brought to the surface, and consequently 
the banks present a denuded surface (Fig. 2). This loose soil 
composing the banks is a favorable habitat in which weeds 
readily establish themselves. As a result, in a very few years, 
a new ditch, unless grazed, is densely overgrown with many 
species of weeds. The species of weeds represented on ditch 
Fig-. 2 — A ne-wly constructed ditch. Tlie banks present a denuded surface, and 
a favorable situation in whicli -v\^eeds may establish themselves. 
banks are those inhabiting the roadsides and fields of the 
locality. On account of the water supply along ditches, the 
stand of weeds along them is denser ami the individual plants 
are larger than along roadsides and in waste t)hi(*es. (Fig fi.) 
