GRASSES OF IOWA. 79* 



because of its admixture in other more valuable forage plants, 

 but its direct introduction as a forage plant. Johnson grass 

 [Aiidropogon sorghum var. halapensis), has been widely distrib- 

 uted in the southern states since its introduction as a forage 

 plant in South Carolina, about 1830, by Governor Means. Ten 

 years later it was introduced into Alabama by Captain William 

 Johnson. Since thtn it has been widely distributed throughout 

 the south, where in some places it has become an execrable 

 weed. It has advanced as far north as central Missouri, where 

 it was introduced with seeds in part grown as a forage plant. 



Another grass that has been distributed largely by human 

 agencies is the Bermuda grass, introduced in this country first 

 as ballast, from southern Europe. It has now spread over the 

 entire southern states, and although a most valuable grass, is 

 a dangerous weed when grown where not wanted. A few 

 years ago we found, on the college grounds, the Bromus tecto- 

 rum, the seed of which came with some packing material. 

 Instances of this kind might be given much more extended 

 notice in this connection. One other case is worthy of men- 

 tion; Wild oats {Avenafatua), which has become widely distrib- 

 uted in Iowa, Wisconsin and Minnesota, occurring commonly 

 as a weed in oat and wheat fields, but generally in oat fields. 

 It is impossible to remove the seed of this species from oats. 

 In the Rocky Mountain districts, wild oats is extremely com- 

 mon and this species was introduced in the same way. In 

 California there are several pernicious species of Avena that 

 were introduced with grain seed. 



GERMINATION. 



St7'ucture of the embryo. — After the seed has been distributed, 

 the next important step is germination. The small embryo is 

 usually straight, rarely slightly bent with the radicle turned 

 downwards. The following is taken from Hackel's excellent 

 account: " Its most striking portion is the scutellum, which 

 is regarded as the cotyledon. It is a fiat but somewhat thick 

 body, roundish to elongated oval in circumference, lying close 

 on its inner side to the albumen, with the plumule and radicle 

 surrounded by the coleorhiza situated in its somewhat shallow 

 exterior. The plumule lies free upon the scutellum, but below 

 the plumule the axis of the embryo is united with it. This is 

 the point of insertion of the scutellum beyond which it pro- 

 jects downward and outward as far as the point of the coleo- 



