background articles and reviews:
Campbell, N. A. Biology (third edition). New York: The Benjamin/Cummings 
       Publishing Company, Inc. pp. 575-576, 736-740. 1993. 
Cheung, A. Y. Pollen-pistil interactions during pollen-tube growth.
       1: 45-51. 1996.
Fosket, D. Plant growth and development: a molecular approach. San Diego:
       Academic Press. pp. 413-417. 1994.
Kao, T. H. and McCubbin A. G. How flowering plants discriminate between
       self and non-self pollen to prevent inbreeding. Proceedings of
       the National Academy of Sciences. 93: 12059-12065. 1996.
Newbigin, E, Anderson, M. A. and Clarke, A. E. Gametophytic self-
       incompatibility systems. The Plant Cell. 5: 1315-1324. 1993.
Taylor, L. P. and Hepler, P. K. Pollen germination and tube growth.
       Annual Review of Plant Physiology and Plant Molecular Biology.
       48: 461-491. 1997.
Westhoff, P. (ed.) Molecular plant development: from gene to plant. Oxford:
       Oxford University Press. pp.208-215. 1998.
articles:
Dodds, P. N., Bonig, I., Du, H., Rodin, J., Anderson, M.A., Newbigin,
       E., and Clarke, A. E. S-RNase gene of Nicotania alata is expressed
       in developing pollen. The Plant Cell. 5: 1771-1782. 1999. 
Golz, J. F., Su, V., Clarke, A. E. and Newbigin, E. A molecular description
       of mutation affecting the pollen component of the Nicotania alata
       S locus. Genetics 152: 1123-1135. 1999.
Ishimizu, T., Sato, Y., Saito, T., Yoshimura, Y., Norioka, S., Nakanishi,
       T. and Yoshimura, F. Identification and partial amino acid sequence of
       seven S-RNases associated with self-incompatibility of Japanse pear,
       Pyrus pyrifolia Nakai. Journal of Biochemistry. 120: 326-334. 1996.
Ishimizu, T., Norioka, S., Kanai, M., Clarke, A. E. and Sakiyama, F. Location
       of cysteine and cystine residues in  S-ribonucleases associated with
       gametophytic self-incompatibility. European Journal of Biochemistry.
       242: 627-635. 1996.
Lee, H. S., Huang, and S., Kao, T. H. S proteins control rejection of
       incompatible pollen in Petunia inflata. Nature. 367: 560-563. 1994.
Lush, W. M. and Clarke, A. E. Observations of pollen tube growth in Nicotania
       alata and their implications for the mechanism of self-incompatibility.
       Sexual Plant Reproduction. 10: 27-35. 1997.
Murfett, J., Atherton, T. L., Mou, B., Gasser, C. S. and McClure, B. A.
       S-RNase expressed in transgenic Nicotania causes  S-allele-specific
       pollen rejection. Nature. 367: 563-566. 1994.
Royo, J., Kunz, C., Kowyama, Y., Anderson, M., Clarke, A. E. and Newbigin, E.
       Loss of a histidine residue at the active site of S-locus ribonuclease
       is associated with self-compatibility in Lycopersicon peruvianum. 
       Proceedings of the National Academy of Sciences. 91: 6511-6514. 1994.
Sassa, H., Hirano, H., Nishio, T. and Koba, T. Style-specific self-
       compatible mutation caused by deletion of the S-RNase gene in 
       Japanese pear (Pyrus serotina). The Plant Journal. 12:223-227. 1997.
Walles, B. and Han, S. P. Ribosomes in incompatible pollen tube in the 
       Solanaceae. Physiologia Planatarum. 103:461-465. 1998.