ECONOMIC IMPORTANCE OF GREEN PLANTS 127 



by cold, other insects prey on them, but at the present time they 

 are one of the greatest pests the south knows. 



The control of this pest seems to depend upon early planting so 

 that the crop has an opportunity to ripen before the insects in the 

 boll grow large enough to do harm. Ultimately the boll weevil 



Mexican cotton boll weevil. Much enlarged, above; natural 



size, below. (Herrick.) 



may do more good than harm by bringing into the market a type 

 of cotton plant that ripens very early. 



Vegetable Fibers. — Among the most important are Manila 

 hemp; which comes from the leaf-stalks of a plant of the banana 

 family and true hemp, which is the bast or woody fiber of a plant 

 cultivated in most warm parts of the earth. Flax is also an im- 

 portant fiber plant, grown largely in Russia and other parts of 

 Europe (see picture on next page) . From the bast fibers of the 

 stem of this herb linen cloth is made. 



Vegetable Oils. — Some of the same plants which give fiber 

 also produce oil. Cotton seed oil pressed from the seeds, linseed 

 oil from the seeds of the flax plant, and coconut oil (the covering 

 of the nut here producing the fiber) are examples. 



Some Harmful Green Plants. — We have seen that on the whole 

 green plants are useful to man. There are, however, some that 



