Oct. 1, 1919-Mar. IS, 1920 Illustrations IX 



Page 

 'Plate 20. A. — Cross section of the tip of a very young cob. B. — Portion of a 

 cross section of a young cob just back of the tip, showing the rudiment or 

 primordium from which a pair of spikelets will develop. C. — Cross section 

 of a rudiment at the beginning of its division into equal parts. D. — Cross 

 section of a pair of spiklets in the process of development 266 



Plate 21. A. — Longitudinal section of the tip of a young cob. B. — Longitu- 

 dinal section of the rudiment or primordium of a spikelet just back of the 

 tip of a young cob : g, primordium of the lower empty glume. C. — Longi- 

 tudinal section of the developing spikelet, showing the primordia of the 

 lower and upper empty glumes: g, lower empty glume; g'', upper empty 

 glume. D. — Longitudinal section of the developing spikelet at a little 

 later stage than C: g, lower empty glume ; g^, upper empty glume 266 



Plate 22. A. — Longitudinal section of the developing spikelet: g, lower 

 empty glume; g'', upper empty glume; 1, primordium of the lemma or flow- 

 ering glume of the fertile flower; V, primordium of the lemma or flowering 

 glume of the sterile flower; sf , primordium of the sterile flower. B. — Longi- 

 tudinal section of the developing spikelet: g and g^, empty glumes; 1 and 

 V, lemmas or flowering glumes; sf, primordium of the sterile flower; st, 

 stamen of the fertile flower; p, palet of the fertile flower; pp, primordium of 

 the pistil 266 



Plate 23. A. — Longitudinal section of the developing spikelet at the time 

 the carpel or ovary wall has begun to develop : g and g'', empty glumes; 1 and 

 V, lemmas; sf, sterile flower; p and p', palets; st, stamen; c and c^, rudi- 

 ment of the carpel or ovary wall ; c' is the more rapidly growing part of the 

 carpel. B. — Longitudinal section of a developing ovary: c and c^, devel- 

 oping ovary walls; c^ is the portion of the carpel from which the style or 

 silk will develop ; ov, ovule ; ovc, primordium of the inner ovule coat 266 



Plate 24. A. — Longitudinal section of the fertile pistil at the time the silk has 

 started to elongate: ovw, ovary wall; sc, stylar canal; ovc, ovule coats; ov, 

 ovule; ms, megaspore mother cell; sk, silk. B. — Longitudinal section of 

 the fertile pistil at the time the ovule has started to invert: ovw, ovary 

 wall; sc, stylar canal; sk, silk; ovc, ovule coats; ms, megaspore-mother cell . . 266 



Plate 25. A. — Longitudinal section of the inverted ovule: ov, ovule; ovc, 

 ovule coats; es, embryo sac; mic, micropyle; co, cavity of ovary. B. — Sec- 

 tion through the stylar canal, showing its structure shortly before the silk 

 emerges froin the husk 266 



Plate 26. A. — Cross section of the megaspore mother cell. B. — Longitudinal 

 section of the megaspore mother cell. C. — I/jngitudinal section of the 

 2-celled embryo sac 266 



Plate 27. A. — Longitudinal section of the 4-celled embryo sac. E. — I,ongi- 

 tudinal section of an 8-celled embryo sac at the time the polar nuclei have 

 started to migrate. C— lyongitudinal section of an 8-celled embr>'o sac 

 after the polar nuclei have migrated 266 



Plate 28. Ivongitudinal section of a mature embryo sac just previous to fertili- 

 zation: e, egg; sy, synergids; p, polars; ant, antipodals; pt, pollen tube; 

 m, micropyle; v, vacuole; c, cytoplasm; ov, ovule coat 266 



Plate 29. A. — End of a silk: p, pollen grains; v, fibro-vascular bundles; h, 

 hairs. B . — Tips of the hairs of the silk . C . — Section of a pollen grain show- 

 ing the germ pore and the relative size of the vegetative and sperm nuclei. 

 D. — Single hair of the silk, showing the general manner in which the pollen 

 tube penetrates the sheath cells of the fibro-vascular bundle of the silk: 

 p, pollen grain; h, hair; pt, pollen tube; sc, sheath cells of the fibro-vascu- 

 160116°— 21 2 , 



