52 BOTANICAL GAZETTE [july 



8. Cannon, W. A., Physical relation of roots to soil factors. Carnegie 

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9. , Root variation in desert plants. Plant World 16:323-341. 1913. 



10. , Evaluation of the soil temperature factor in root growth. Plant 



World 21:64-69. 1918. 



11. Cannon, W. A., and Free, E. E., The ecological significance of soil aera- 

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12. Craig, J., Root killing of forest trees. Iowa Exper. Sta. Bull. no. 44. 1899. 



13. Dachnowski, a.. Toxic properties of bog water and bog soil. Bot. Gaz. 

 46:130-143. 1908. 



14. , Bog toxins. Box. Gaz. 47:389-405. 1909. 



15. — — — , Cranberry Island. Box. Gaz. 52:1-33. 1911. 



16. Freidenfeldx, T., Studieniiber die Wurzelnkrautiger Pflanzen. I. Flora 

 91:115-208. 1902. 



17. , Studien iiber die Wurzeln krautiger Pflanzen. II. Bibl. Bot. 



61: 1904. 



18. GoFF, E. S., Study of roots of certain perennial plants. Wis. Agric. Exper. 

 Sta. Report no. 14. 286-298. 1897. 



19. Hellriegel, H., Beitrage zu den Grundlagen des Ackerbaus. Braun- 

 schweig. 1883. 



20. HiLGARD, E. W., Soils. 1906. 



21. HrfcHCOCK, A. S., Studies on subterranean organs. I and II. Trans. 

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22. HovELER, W., Uber die Verwerthung des Humus bei der Ernahrung der 

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23. King,"F. H., Natural distribution of roots in field soils. Wis. Sta. Report 

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24. Kroemer, K., Wurzelhaut, Hypodermis, und Endodermis der Angio- 

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25. NoBBE, F., liber die feinere Verastelung der Pflanzenwurzeln. Landw. 

 Versuchstationen 4:212-224. 1862. 



26. NoYES, H. A., Trosx, J. F., and Yoder, L., Root variations induced by 

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27. Pammel, L. H., Weeds of the farm and garden. New York. 191 1. 



28. Pulling, H. E., Root habit and distribution in the far north. Plant World 

 21:223-233. 1918. 



29. RiGG, G. B., Decay and soil toxins. Box. Gaz. 61:295-310. 1916. 



30. RiMBACH, A., Contractile roots. Abstr. in Bot. Centralbl. 74:209-211. 

 1898. 



31. Roxmisxrov, v.. Nature of drought. Relation of root systems to soil and 

 drought. Reviewed in E.S.R. 1914. 



32. RuscHE, E.. Beeinflussung der Keimfahigkeit verschiedener Kulturpflanzen 

 durch Salzdiingung. Jour. Landw. 60:303-365. 191 2. 



