2o Minnesota Plant Life, 



some dim notion of secretiveness or possibly of providence. 

 On account of the rhythm of the seasons in Minnesota the 

 principal migrations of birds and land animals have not been 

 from east to west but from north to south, and the principal 

 tension-line runs in general from east to west. 



Insects and worms. A few seeds are peculiarly modified 

 for insect distribution, as for example, those of some spurges 

 and other small plants, which have little crests or grooves just 

 fitted to receive the jaws of ants, thus making them easily porta- 

 ble by these busy toilers. Others are assisted in their distribu- 

 tion by burrowing worms, but this always within narrow limits. 



Inanimate agencies. Allusion has already been made to the 

 inanimate agencies which are employed by plants as aids in 

 distribution. Among these are currents of wind, currents of 

 water and in a slight degree translocations of soil. The latter, 

 best observed in mountainous regions where avalanches exert 

 a considerable influence, is of slight importance in Minnesota, 

 though upon the hillsides and cliffs along some of the northern 

 lakes, this method of distribution exists. 



Wind currents. In plant distribution the most important 

 inanimate agency is doubtless the wind. The alertness with 

 which plants make use of it in seed-dissemination is well exem- 

 plified by the new population which appears after a fire and 

 covers burnt places in the forest. When the pines or spruces 

 are destroyed by fire it is a fact of common observation that 

 poplars, maples, elms, willow-herbs, milkweeds and other light- 

 seeded plants spring up. The well-known fire-weed with its 

 purple panicle of flowers ripens seeds that are provided with 

 tufts of delicate hairs, and when thrown out of the pods in which 

 they are produced the wind may catch them and whirl them 

 away over the tree-tops for many miles. The poplars, too, and 

 cottonwoods are famous for their winged seeds and succeed in 

 entering promptly a burnt tract, so that within a year or two 

 they have established themselves while there are yet to be found 

 probably none of the heavy-seeded plants, like hickories, wal- 

 nuts and oaks, and but few of the plants with adhesive seeds 

 or pulp-inclosed seeds fitted for animal distribution. It is not 

 the seeds alone but often the fruits of plants which are trans- 

 ported by the wind, as for example, the maple-fruits, the elm- 



