X Journal of Agricultural Research voi. xviii 



Page 

 lar bundle. E. — T/)ngitudinal section of a fibro-vascular bundle of a silk, 

 showing the position of the pollen tube as it grows down the silk : sc, sheath 

 cells; X, xylem elements; p, parenchyma cells of the silk; pt, pollen tube, 

 showing the enlarged tip 266 



Plate 30. A. — Cross section of a silk jiear its base, showing the position of the 

 fibro-vascular bundles. B. — Cross section of a fibro-vascular bimdle of the 

 silk: X, xylem elements; sc, sheath cells; pt, pollen tube. C. — Ixjngitu- 

 dinal section through the sheath cells of the fibro-vascular bundles: sc, 

 sheath cells; pc, parenchyma cells of the silk 266 



Plate 31- A. — Vegetative and sperm nuclei of the pollen grain: vn, vegeta- 

 tive nucleus; sn, sperm nuclei. B. — Longitudinal section of the lower por- 

 tion of the embryo sac at the time of fertilization, reconstructed from two 

 sections: pn, polar nuclei fusing; sn^, sperm nucleus fusing with a polar 

 nucleus; e, egg; sn, sperm nucleus in the egg; pt, pollen tube; syn, 

 synergid; v, vacuole 266 



Plate 32. A. — Longitudinal section of the embryo sac 12 hours after fertili- 

 zation: end, endosperm nuclei; e, egg in which one of the daughter nuclei 

 ha? already divided; ant, antipodals. B. ^Longitudinal section of the 

 embryo sac 36 hours after fertilization: end, endosperm; emb, embryo, 

 ant, antipodal tissue. C. — Ix)ngitudinal section of the young embr^^o at 

 the stage shown in B 226 



Response of Citrus Seedlings in Water Cultures to Salts 

 AND Organic Extracts 



Plate ss- A. — Grapefruit roots, 12 days old, grown in distilled water. B. — 

 Grapefruit roots, 12 days old, grown in distilled water plus 100 parts per 

 million water-soluble peat. C. — I^emon seedlings, 21 days old, grown in 

 carbon-treated distilled water. D. — Lemon seedlings, 21 days old, growTi 

 in carbon-treated distilled water plus calcium carbonate. E. — Grapefruit 

 seedlings, 20 days old, grown in carbon-treated water. F. — Grapefruit 

 seedlings, 20 days old, grown in carbon- created water plus calcium carbo- 

 nate 274 



Plate 34. A. — Lemon seedlings, 16 days old, gro^^'n in distilled water as con- 

 trol. B. — I,emon seedlings, 16 days old, grown in 400 parts per million 

 sodium carbonate. C. — Lemon seedlings, 16 days old, grown in 100 parts 

 per million ammonia-soluble humus. D. — Lemon seedlings, 16 days old, 

 growm in 100 parts per million ammonia-soluble humus plus 40c parts per 

 million sodium carbonate. E. — Citrus seedlings grown in carbon-treated 

 water. F. — Citrus seedlings grown in 4/10 per cent sodium nitrate (NaNOs). 

 G. — Citrus seedlings grown in 4/10 per cent sodium nitrate with calcium 

 carbonate (CaCOs) 274 



Physiological Study of the Parasitism of Pythium debaryanum 

 Hesse on the Potato Tuber 



Plate 35. A. — Ajjparatus used in determining the pressure required to punc- 

 ture the tissue of potato tubers. B. — Glass rod with attached needle 298 



Plate 36. Photographs enlarged from portions of a motion photomicrograph, 

 showing the method of cell wall penetration b}'^ Pythium hyphae. A. — 

 Shows hypha growing toward the potato cell wall. B. — Shows hypha at- 

 tached to wall and about to penetrate . C . — The tip has just broken through 

 the wall. D. — The penetration is complete 298 



