486 BOTANICAL GAZETTE [DECEMBER 
7. DEVrIEs, H., Species and varieties; their origin by mutation. Chicago. 
1905. 
- 
, The coefficient of mutation in Oenothera biennis L. Bor. Gaz. 
59:169-196. IgI5. 
9. Dorsey, M. J., Pollen development in the ieee: oe special reference to 
pollen sterility. Univ. Minn. Exp. Sta. Bull. no. 144. pp. 50. 1914. 
to. DutrocHet, R. J. H., The sterility of hybrid oa Gard. Mag. 8:500. 
1832 
32. 
11. ENGLER, A., and PRANTL, re Die natiirlichen Pflanzenfamilien. 3:208 
12. GaTEs, R. R., Pollen development in hybrids of Ocenothera lataXO. 
Lamarckiana, wat its relation to mutation. Bor. Gaz. 43:81-115. 1907. 
, Hybridization and germ cells of Oenothera mutants. - Bor. Gaz. 
4421-12. 1907. 
, Pollen formation in Oenothera gigas. Ann. Botany 25:909-940. 
IQII. 
15. GrecorY, E. S., Pollen of hybrids. Jour. Bot. 45:377-378. 1907. 
16. GUIGNARD , L., Observations sur la stérilité comparée des organes repro- 
ducteurs, Ses Sybiks végétaux. Bull. Soc. Bot. Lyon 4:66-78. 1887. 
17. HAUSSKNECHT, C., Monographie der Gattung Epilobium. 1884. 
18. eEraNy, E. C., The mutation myth. Science 39:488—491. 1914. 
1 objections to the mutation theory 
9- 4 
of DeVers. Amer. Nat. 49: ide, IQI5. 
20. ———, Spore conditions in hybrids and the mutation hypothesis of 
DeVries. Bor. Gaz. 58:322-336. 1914. 
21. MEEHAN, T., Sterility of violets. Bot. Gaz. 14:200. 1889. 
22. SMITH, W. G., Notes on pollen. Gard. Chron. 7:516-517, 547-549: 1876. 
23. Tiscuer, G., Uber die Entwicklung der Sexualorgane bei einem sterilen 
Brvonia Bastued. Ber. Deutsch. Bot. Gesells. 24:83-96. pl. 7. 1906. 
EXPLANATION OF PLATES XIX-XXI 
Fic. 1.—Epilobium angustifolium L., showing entirely fertile pollen; <75. 
Fic. 2.—E. angustifolium L., showing perfectly developed pollen grains;. 
x12 oe 
3.—E. angustifolium L., showing no indication of abortion due to 
hae. X 150. 
Fic. 4.—E. angustifolium L., showing fertile pollen; 140. 
Fic. 5.—E. angustifolium L., showing abortive pollen; 125. 
Fic. 6.—E. angustifolium L., showing fertile and abortive pollen, and a 
single tetrad in which all the grains are defective; 125. 
Fic. 7.—E. angustifolium L., soe indications of hybridism, as shown 
by the degenerate pollen grains 
Fic. 8.—E, ongustifotaim 1 . Sovaie fertile and infertile microspores; 
X 200. 
