WEEDS OF MONTANA. 



to scatter their seeds. By far the larger part are annuals 

 and are hence unable, when left to their own resources, to long 

 compete with the more enduring native species. Biennials are 

 particularly weak, being unfitted for the annual upturning of the 

 soil in cultivation or for extended contests with the perennial 

 species, finding their natural conditions only in waste places and 

 along highways. Weeds must also contend in unceasing passive 

 warfare with man, whose interests the}- endanger, but who pro- 

 vides them with conditions best suited for their growth. 



MEANS OF DISTRIBUTION. 



Weeds, like other plants, are dependent upon physical agencies 

 for the distribution of their seed, but rely more largely upon man 

 and domestic animals for this aid. It may be well to enumerate a 

 few of the principal means thus employed. 



A considerable number of species depend upon the wind to 

 scatter their seeds and such w r eeds produce feathery, hairy or 

 winged seeds or have their seed envelopes so modified as to aid in 

 such dissemination. Among these are the thistles, fireweed, 

 dandelion, milkweed, sow-thistle and rag weed (Erigeron), while 

 the docks, penn\xress and orache are likewise assisted by their 

 winged fruit pods and appendages. Again, a group of plants 

 called "tumble-weeds," adapted particularly to the plains, grow in 

 large globular clusters and have the curious habit of breaking 

 loose from the ground in the winter and are then rolled about over 

 the country by the wind, scattering their seeds throughout their 

 course. We have here the tumble-weed (Amaranthus albus), the 

 tumbling mustard (Sis\ r mbrium altissimum) and the Russian 

 thistle (Salsola Kali Tragus), while the tumble-grass (Panicum 

 capillare) is found to some extent eastward. 



Another large class depends more particularly upon the water 

 for seed transportation and such seeds have light, water -proof 

 envelopes, which enable them to float for considerable distances 

 before saturation. Indeed, the seeds of nearly all weeds are thus 

 distributed to a greater or less extent, but the sunflower, the 

 horse- weed (Iva), wild mustard, pigweeds and the sweet clover 

 seem to depend mainly upon irrigation for their spread, and the 

 docks come largely under the same class. 



