Feb., 19 IS] 



Sexual Dimorphism 



115 



The next step in the evolutionary progression of sexual 

 dimorphism may be represented by Indian-corn, Zea mays L. 

 Here as is well known the typical plant has a terminal staminate 

 inflorescence, and one or more carpellate inflorescences devel- 

 oped from the side of the stem. (Figs. IG and 17). The differ- 

 ence between the two branches is remarkable although they 

 consist of the same morphological elements. The carpellate 

 branch shows by far the greater deviation from the general 

 vegetative morphology.' The main differences are as follows: 



Staminate stem. 



1. Normal internodcs. 



2. Normal sheaths. 



3. Leaf blade normal. 



4. Inrtorescence of comparatively 

 primitive type, branched. 



5. Axes normal. 



6. Character of glumes, membranous 



and elongated. 



7. Staminate flower. 



8. Little or no vestige of gynecium. 



9. Normal stamens. 



10. Microsporangia, 



11. Microspores. 



12. Ordinary color in floral axis and 



glumes. 



Carpellate stem. 



1. Intemodes greatly shortened. 



2. Sheaths changed to husks. 



3. Leaf blade absent or vestigial. 



4. Inflorescence modified, with loss of 



branches. 



5. Axis a cob. 



(). Character of glumes, chartaceous 

 and broad. 



7. Carpellate flower. 



8. Remarkable development of style 



and stigmas (Silk). 



9. Minute or no vestiges of stamens. 



10. Megasporangia. 



11. Megaspores. 



12. In some varieties, red or other color 



in floral axis and glumes. 



The writer recently received an interesting ear of popcorn 

 from Mr. L. E. Thatcher which shows a zonal arrangement of 

 the sexual condition. This ear is a normal side ear with the 

 lower part typically developed. In the middle is a complete 

 zone, about an inch long, of staminate spikelets, while the 

 outer part is typical ear structure again with normal grains. 

 In this case there is a successive reversal of the growing axis. 

 First the axis develops a cob with normal carpellate spikelets, 

 then changes suddenly to a staminate condition and finally 

 resumes its growth in the carpellate state. 



The buffalo-grass, Bulbilis dactyloides (Nutt.) Raf. is a 

 perennial, monecious grass with stolons which root at the 

 nodes. According to Plank* and to Hitchcockf any given node 

 produces but one type of inflorescence, and each kind of stolon 

 is supposed to propagate its own kind. If this is true, the 

 buffalo-grass would be an interesting plant for experimentation. 



*Plank, E. N. Buchloe dactyloides Engelm. not a Dioecious Grass. Bull. 

 Torr. Bot. Club. 19 : 303. 1892. 



fHitchcock, A. S. Note on Buffalo Grass. Bot. Gaz. 20 : 464. 1895. 



