88 GRASSES OF IOWA. 



days), need fourteen days, and Abietineas, twenty- one days. 

 Gilbert H. Hicks* gives the germinative energy for cereals, 

 clovers, peas, vetches, flat peas, flax, dodder, poppy, Brassica, 

 Lepidium, radish, spiirry and chicory at three days. For 

 ordinary field conditions this is somewhat too short a period. 

 In laboratory and greenhouse our tests show that corn requires 

 five or six days as an average. 



The time required for germination varies greatly. This 

 depends largely upon external conditions. Sachs has given 

 us the following temperature required for germination: 



OPTIMUM. MAXIMUM. MINIMUM. 



Zea mays (corn) 33c 46c 9 . 5 



Triticum vulgare (wheat). . . 29 42 5 



Hordeum vulgare (barley) , . 29 38 5 



Haberlandt gives as the maximum temperature of germina- 

 tion of cereals the following: Wheat, 31-37 C; rye, 31-37 C; 

 barley, 31-33 C; oats, 31-37 C; corn, 44-50 C; millet, 44-50 C. 



He has determined the minimum temper iture and rapidity 

 of germination as f jUows: Time of counting when caulicle 

 appeared : 



4.75 C. 10.5 C. 15.6 C. 18.5 C. 



Winter wheat 6 3 2 1.75 



Winter rye 4 2.5 1 1 



Barley 6 3 2 1.75 



Corn 11.25 3.25 3 



English rye grass 10 5.5 3.75 3 



Timothy 6.5 3.25 3 



O. Burchard has made the following determination of grass 

 seed and temperature: 



Germination after 



days 



Poa pratensis, per 



cent. 



Poa trivialis, per 



cent. 



Poa nemoralls, per 



cent. . 

 Poa annua, per ct. . 

 Poa compressa, per 



cent . . 

 Agrostls stolonlfe- 



ra. percent. 

 Alopecurus praten- 

 sis, per cent 



CONSTANT TEMPERATURE, 



68° F. 



5.06 



16.17 



8.75 

 54 9 



0.0 



58.5 



9.75 



7 



13.89 



39 87 



18.58 

 76.33 



17 



63.92 



30.67 



14 

 24.39 

 69.33 



26.33 



74.83 



0.5 

 64.59 

 Qi.5 



28 



25.72 



71 33 



27 13 

 75.17 



0.67 



64.75 



71 92 



CONSTANT TEMPERATURE, 



6.45 

 19.83 



7.0 



56.83 



0.0 



78.17 

 8.08 



7 



10.11 



31.83 



13.5 

 68.0 



1 67 



83.33 



30.84 



14 

 12 28 

 33.25 



17.43 



72.83 



3.33 

 84.59 

 59 75 



31 



13.61 



39.17 



17.59 

 73.67 



3.33 



85.0 



84.34 



28 



12.61 



40.0 



17.59 

 7S.87 



3.33 



89.0 

 65.15 



♦Year Book. U. S. Dept. of Agrl. 1894: 399. 



