GRASSES OF IOWA. 



55 



more or less, in Indian corn; seven days, more or less, 

 in timothy, several days in oats and wheat, and for a much 

 longer period in branching grasses like Eragostis and Muhlen- 

 bergia. " Several grasses produce what are known as cleistog- 



amous flowers. AmpJd- 

 carpum purshii, indigen- 

 ous to New Jersey and 

 southward, produces two 

 kinds of flowers. Those 

 with open flowers sterile, 

 "vshile those borne on the 

 small runners at the base 

 of the culms are abund- 

 antly fertile. Leersia 

 oryzoides produces cleitso- 

 gamous flowers. 



Gross- ferti lization. — 

 Hackel has shown that 

 cross-feriilization is much 

 more rare and difficult in 

 barley, and in certain 

 races like the six-ranked, 

 the short spiked two- 

 ranked and the peacock 

 barley, the flower of the 

 grasses, especially in 

 some climates, never 

 open and consequently 

 cross-fertilization is im- 

 possible. Wheat is also 

 pollinated in the bud dur- 

 ing cloudy and rainy 

 weither. In ryr , on the 

 other hand, the rule is to have the flowers cross-pol inated. 

 They have in fact lost the power of self pollination. Cross-ferti- 

 lization takes pla^e read ly in nature as shown in numerous 

 forms of corn, such as sweet, pop, dent and flint. Corn is 

 remarkable in showing the immediate eifect of cross-fertiliza- 

 tion or xenia the first season, though it is also evident* in 

 succeeding generations. 



* Just as I am reading proof there has come to hand a valuable paoer on Xenia, by 

 Webber. BaU. U. S. Depo. of A^r. Div. of Veg. Path, and Veg. Phys. 32: 1900. 



Pig. 44 A. Splkelet of wheat showing glumes, 

 palet, stamens and pistil. {After Saunders.) 



