GRASSES OF IOWA. 77 



panicle. One of my special students, at my suggestion, has 

 made a few experiments to deter jaiae the mode in which the 

 seed escapes. Inside the ovary and about the seed there is a 

 gummy secretion. "When about ready to escape or at a certaia 

 stage of maturity, if water be applied to the panicle, in a short 

 time the seeds come forth. A part of the panicle was wet and 

 in thirty minutes twenty-seven seeds escaped. In another case 

 the seed began to escape in ten minutes after the water was 

 applied. Af ler drying six days in a room seeds started out in 

 twenty minutes after wetting. In other cases seeds have been 

 seen to escape in six minutes and in one case in four and one- 

 half minutes. If the ovary is carefully removed from the 

 floral glume and palea and water is applied, the seeds usually 

 escape a little quicker than when left in the floret. " 



"On applying water the ovary may be seen to slowly enlarge, 

 till it bursts and the seed pops out in a hurry. If a little 

 water is applied, it moves more slowly, and if the glumes are 

 still near the ovary the seed moves upward and usually 

 adheres to some part of the panicle. A slight sprinkling or a 

 heavy dew would bring the seeds out, but a heavy rain would 

 wash them down at a time when the condition would be favor- 

 able for germination. Several other species, as I judge from 

 herbarium specimens, expel and hold their seed in a similar 

 manner. The action of the water on the ovary seems to be 

 purely mechanical and is explained in well known works on 

 physics. The water enters tbe ovary faster than the gum can 

 escipe. The ovary is flattened and splits on the side next the 

 palea. " The gum spoken of by Beal is a mucilage and resides 

 in the outer walls of the cells of the capsules that swell on the 

 addition of water. 



Man, too, is an agent in the scattering of the seeds of 

 grasses and the introduction of new seeds. Certain grasses 

 most commonly follow the culture of certain grains, as chess 

 and its occurrence in wheat fields. 



It is a well known fact that chess is more abundant where 

 wheat is extensively cultivated, and there is no question that 

 this weed was introduced by the wheat seed brought from 

 Europe Darlington* observes, "This foreigner is a well 

 known pest among our fields of wheat and rye and occasion- 

 ally appears in the same field for a year or two after the grain 

 crop. Years ago it was observed that this weed was common 



♦American Weeds and Useful Plants, Rerised by George Thurber. New York. 386. 



