BIOLOGICAL PAPERS 199 



to many a Northern farmer, on account of its dissemination of seeds 

 by means of the wind as well as its spreading by deep-running roots. 



But not only are single seeds carried by the winds, but whole flower 

 clusters at times, when ripe. The "Russian thistle" {SaUola kali 

 var. tragus) — saltwort — which, in reality, is not a thistle at all, but 

 an "immigrant" without which we would be much better off, has 

 wings on the back of the fruiting calyx. It sometimes forms large, 

 bushy masses which, when dry, are driven by the wind in such quan- 

 tities that they form ridges as high as fences. One such plant has 

 been estimated to carry with it as many as 200,000 seeds. It "was 

 first introduced into South Dakota in flaxseed brought from Russia 

 and planted in 1873 or 1874. In twenty years from that time the 

 plant had become one of the most formidable weeds known over an 

 area of about 25,000 square miles." - 



Other seeds are supplied with wings for flying, as the smara of the 

 maple {Acer Tourn.), White ash {Fraxinus americana L.), elm 

 {Dlmus L.), etc. Of the American linden {Tilia americana L.), 

 the fruit is attached to a foliaceous bract which carries it through the 

 air. The maple seeds fall from the trees with a twirling motion, 

 which is especially designed to help carry them a greater distance. 

 In some species of the Pinus (pine) the multiple fruit is in the form 

 of a cone or strobile, the scales of which, when ripe and dry, turn 

 back or separate, and the seed, with a lining of the scale, is dispersed 

 by the wind. The pine-cones are sometimes opened by frosts. In 

 damp weather they are seen to be closed. 



A second mode of transportation is by water. Many seeds are pro- 

 vided with an impervious outer coat and a light, porous one. An ex- 

 ample is the cocoanut. In the formation of coral islands, after the 

 polyps and waves have done their wonderful work, floating wood 

 lodges among the coral fragments, which decays and forms mold. 

 Seeds, such as cocoanuts, which are not injured by the salt-water, are 

 carried thousands of miles by the waves and deposited on the islet, 

 and soon produce the cocoa- palm (Cocos nucifera). Rivers and 

 creeks carry walnuts, hickory-nuts, cockle-burs and the catkins of 

 birch with them and deposit these seeds along their banks. 



Man has been an active agent in the dissemination of seeds ; more 

 especially was this the case in the years of the settlement of America. 

 The immigrants brought cereals with them to this country, and 

 took back the "Irish" potato {Solanum tuberosum), from Chili, 

 South America ; the tomato {Lycopersicum esculentum) , from tropical 

 America; tobacco {Nicotina tabacum L.), which is named for John 

 Nicot, one of the introducers of tobacco into Europe ; and Indian 

 corn or maize {Zea mays), from Paraguay. 



2. Bergen, Elements of Botany, pp. 201 and 205. 



