Adiku, G.K.S., Ozier-Lafontaine, H., and Bajazet, T., 2001. Patterns of root growth and water uptake of a maize-cowpea mixture grown under greenhouse conditions. Plant and Soil 235: 85–94.
Birt, D.F., Widrlechner, M.P., Hammer, K.D.P., Hillwig, M.L., Wei, J.Q., Kraus, G.A., Murphy, P.A., McCoy, J.A., Wurtele, E.S., Neighbors, J.D., Wiemer, D.F., Maury, W.J., and Pric, J.P., 2009. Hypericum in infection: Identification of anti-viral and anti-inflammatory constituents. Pharmaceutical Biology. New York: Informa Healthcare 47(8): 774-782.
Birt, D.F., Widrlechner, M.P., LaLone, C.A., Wu, L.K., Bae, J.H., Solco, A.K.S., Kraus, G.A., Murphy, P.A., Wurtele, E.S., Leng, Q.A., Hebert, S.C., Maury, W.J., and Price, J.P., 2008. Echinacea in infection. American Journal of Clinical Nutrition 87 (2) Bethesda: American Society for Clinical Nutrition 488S-492S.
Brevedan, R.E., and Egli, D.B., 2003. Short periods of water stress during seed filling, leaf senescence, and yield of soybean. Crop Science 43: 2083-2088.
Callan, N.W., Yokelson, T., Wall-MacLane, S., Westcott, M.P., Miller, J.B., and Ponder, G., 2005. Seasonal trends and plant density effects on cichoric acid in Echinacea purpurea (L.) Moench. Journal of Herbs, Spices and Medicinal Plant 11(3) Binghamton: Haworth Herbal Press 35-46.
Cosculleola, F., and Fact, J.M., 1992. Determination of the maize (Zea mays L.) yield functions in respect to water using a line source sprinkler. Field Crops Abstract 93: 5611.
Debaeke, P., and Aboudrare, A., 2004. Adaptation of crop management to waterlimited environments. Europ. Journal of Agronomy 21: 433-466.
Foster, S., 1991. Echinacea: Nature’s Immune Enhancer, Healing Arts Press, Rochester, VT.
Frank, R., Schenk, R., and Nagell, A., 1999. Echinacea pallida (Nutt.) Nutt. - yield and ecidnacoside content. Acta Horticulture 502: 163-166.
Gray, D.E., Pallardy, S.G., Garrett, H.E., and Rottinghaus, G.E., 2003. Acute drought stress and plant age effects on alkamide and phenolic acid content in purple coneflower roots. Planta Medica 69(1) Stuttgart: Georg Thieme Verlag 50-55.
Hobbs, C.B., 1994. Echinacea, a literature review. Herbalgram 30: 33-47.
Javadi, H., 2008. Effect of planting dates and nitrogen rates on yield and yield components of black cumin (Nigella Sativa L.). Iranian Journal of Field Crops Research 6(1): 59-66. (In Persian with English Summary)
Kafi, M., Zand, E., Kamkar, B., Sharifi, R., and Goldani, M., 2000. Plant Physiology. Mashhad Jihad University Press, Iran. 379 pp. (In Persian)
Koocheki, A., and Nassiri Mahallati, M., 1993. Soil and water relations in plants. Mashhad Jihad University Press, Iran. 560 pp. (In Persian)
Laboski, C.A.M., Dowdy, R.H., Allmars, R.R., and Lamb, J.A., 1998. Soil strength and water content influences on corn root distribution in a sandy soil. Plant and Soil 203: 239-247.
Martin, R.J., and Deo, B., 2000. Effect of plant population on Calendula officinalis flower production. New Zealand Journal of Crop and Horticultural Science 28(1): 37-44.
Nesmith, D.S., and Ritchie, J.T., 1992. Short - and long - term responses of corn to a pre - anthesis soil water deficit. Agronomy Journal 84: 107-113.
Norozpoor, G., and Rezvani Moghadam, P., 2006. Effect of different irrigation intervals and plant density on oil yield and essences percentage of black cumin (Nigella sativa). Pajouhesh & Sazandegi. 73: 133-138. (In Persian with English Summary)
Omidbeigi, R., 1995. Approach to Production and Processing of Medicinal Plants. Rahan Nashr Prss, Iran. 424 pp. (In Persian)
Omidbeigi, R., 2001. Investigation and adaptablity cultivation of purple coneflower (Echinacea purpurea) in northern of Tehran. Journal of Agriculture Science. Natur. Resour. 6(2): 231-240. (In Persian with English Summary)
Parmenter, G.A., and Littlejohn, R.P., 1997. Planting density effects on root yield of purple coneflower (Echinacea purpurea (L.) Moench). New Zealand Journal of Crop and Horticultural Science 25 (2): 169-175.
Pol Shekan-e Pahlavan, M.R., Movahedi Naeini, S.A.R., Eatesam, G.R., and Keykha, G., 2008. Wheat plant growth and yield with different planting systems and irrigation frequency 2-soil and plant nutrients. Journal of Agriculture Science Nature Resour 14(5): 51-63. (In Persian with English Summary)
Sarmadnia, G., and Koocheki, A., 1991. Crop Physiology. Mashhad Jihad University Press, Iran. (In Persian)
Sepehri, A., Modares-Sani, S.A., Ghareyazi, B., and Yamini, Y., 2002. The effect of water stress and different levels of nitrogen on the growth, yield and yield components of maize. Iranian Crop Sciences 4: 184-201. (In Persian with English Summary)
Shalaby, A.S., El-Gengaihi, S.E., Agina, E.A., El-Khayat, A.S., and Hendawy, S.F., 1997. Growth and yield of Echinacea purpurea L. as influenced by planting density and fertilization. Journal of Herbs, Spices & Medicinal Plants 5(1): 69-76.
Sirousmehr Member, A., Shakiba, M.R., Aliyari, H., Toorchi, M., and Dabbagh Mohammadinasab. M., 2008. Effects of water deficit stress and plant density on yield and some morphological traits of Autumn-sown safflower cultivars. Pajouhesh and Sazandegi 78: 80-87. (In Persian with English Summary)
Watson, R.R., and Preedy, V.R., 2008. Herbs and infectious diseases. Botanical medicine in clinical practice Wallingford: CAB International 222-227.