i 9 o8] KILDAHL—PHYLLOCLADUS ALPINUS 347 



19. , Studies in the morphology of Torreya califomica. II. The sexual 



organs and fertilization. New Phytol. 3:205-216. pis. y-g. 1904. 



20. Young, Mary S., The male gametophyte of Dacrydium. Bot. Gazette 

 44:189-196. pi. ig. 1907. 



EXPLANATION OF PLATES XX-XXII 



With the exception of figs. 1 and 2 all the figures were drawn with the aid 

 of a camera lucida and reduced one-half. Index letters are as follows: e, endo- 

 sperm; p, perisperm; n, nucellus; if, inner fleshy layer; s, stony layer; of, 

 outer fleshy layer; a, arillus; fs, fleshy scale. 



PLATE XX 



Fig. 1. — Abaxial view of microsporophyll, showing the empty sporangia. 



Fig. 2. — Side view of microsporophyll. 



Fig. 3. — Microspore. X1850. 



Fig. 4. — First division of microspore. X1850. 



Fig. 5. — Two-nucleate stage. X1850. 



Fig. 6. — Second division; first prothallial cell against upper wall. X1850. 



Fig. 7. — Three-nucleate stage, showing form of wings. X3000. 



Fig. 8. — Evanescent walls of the two prothallial cells. X3000. 



Fig. 9. — First evanescent prothallial cell lying outside of the cytoplasm of 

 the spore. X1850. 



Fig. 10. — Mature microspore. X1850. 



Fig. 11. — Microspore with both prothallial cells retained. X3000. 



Fig. 12. — Phylloclad with ovulate strobilus. 



Fig. 13. — Outer view of fleshy scale with ovule. 



Fig. 14. — Inner view of fleshy scale with ovule, showing arillus. 



Fig. 15. — Longitudinal section of ovulate strobilus, showing ovules with 

 integuments, fleshy scales, and position of vascular system, November 1. X40. 



Fig. 16. — Cross-section of ovule; archegonia in the center of the endosperm; 

 November 1. X40. 



Fig. 17. — Longitudinal section of the ovule with fleshy scales; micro pyle not 

 yet formed; arillus covering the ovule; November 1. X40. 



PLATE XXI 



Fig. 18. — Part of nucellus on November 1, showing pollen tubes and part of 

 the female gametophyte in the free nuclear stage; archegonia not yet formed; 

 body cell not yet divided. X850. 



Fig. 19. — Nucellus showing numerous pollen tubes and open archegonia; 

 nearly all the body cells have divided; December 11. X180. 



Fig. 20.— Pollen tube, containing two male nuclei, the stalk and tube nuclei, 

 and one prothallial nucleus, entering the archegonium. X1850. 



Fig. 21. — Archegonial jacket cells. X3000; fig. 21a, same. 



Fig. 22. Fertilization: the fusing nuclei are partially surrounded by the 

 cytoplasmic sheath; the second male nucleus lies above the fusing nuclei and has 

 begun to degenerate. X3000. 



