256 PASTORAL AND AGRICULTURAL BOTANY 



5. The sugar cane crop in the Hawaiian islands was formerly invaded 

 by troublesome weeds. These have been exterminated by covering the 

 planted cane with thick felt paper, which smothers the weeds of the cane- 

 fields, but permits the sharp points of the growing cane stems to push 

 through into the sunlight. The paper used for this purpose was formerly 

 imported into the islands, but is now manufactured out of the fiber ob- 

 tained from the sugar cane stems, that have been through the sugar 

 mills and from which the sugar has been extracted. 



6. Soils are sometimes sour and as a consequence have a particular 

 weed flora, which will disappear, if the land is judiciously treated with 

 lime. 



7. Some weeds flourish in a wet soil,, so that thorough drainage of 

 such soils will lead to the disappearance of the troublesome plants. 



8. The farmer should take the precaution of buying only pure seeds 

 and in having those seeds tested (see next chapter), as many weeds are 

 introduced by the sowing of agricultural seeds containing a considerable 

 number of weed seeds. 



9. It has been suggested without any trial on a large scale that weeds 

 might be exterminated by inoculating them with pure cultures of destruc- 

 tive parasitic fungi. As possible fungi for trial may be mentioned the rust 

 of Canada thistle (Puccinia suaveolens) and the spot disease of smart 

 weed (Septoria polygonum). 



10. The application of chemical herbicides has been tried success- 

 fully in some cases. 



Common Salt (Sodium chloride). This is the cheapest, handiest and 

 safest of herbicides. 



Copperas (Iron sulfate). This chemical is comparatively cheap and 

 as an herbicide. It should be used as a spray. 



Bluestone (Copper sulfate). This is used in solution of twelve pounds 

 of copper sulfate to a barrel of water (52 gallons). 



Carbolic Acid (Phenol). This, because of its cost, can be used only 

 in small areas. 



Caustic Soda (Sodium hydrate). This is better than carbolic acid for 

 killing poison ivy. 



Corrosive sublimate (Mercuric bichloride). One ounce of chemical 

 to six gallons of water. 



Arsenite of Soda. A very active poison used in a solution which is 

 sprayed on the plants. 



