214 MISSOURI BOTANICAL GARDEN. 



Louis some years ago but up to 1907 did not find conditions 

 favorable to the production of a large quantity of seed. How- 

 ever^ since Commelina communis produces large quantities 

 of seed with the utmost ease, the alternative view niiglit be 

 taken that the conditions for germination were exceptionally 

 favorable during the spring of 1908 and that to this must be 

 ascribed its frequency during the present year. The same 

 explanation would apply to the frequency of any one weed 

 during a certahi year. 



The distribution and phenological tables give the names 

 of a number of plants occurring in the section under discus- 

 sion. The nomenclature of Gray's Manual 6 ed. has been 

 followed. The list is not complete but merely aims to give 

 the principal plants. It includes some 850 species, being 

 50% of the phanerogams and vascular ciyptogams occurring 

 within a radius of twenty miles from St. Louis. The present 

 list is based primarily on tlie writer's collections extending 

 over a period of three years as well as on the extensive col- 

 lections of local plants preserved in the herbarium of the 

 Missouri Botanical Garden, notably the collections of the late 

 Dr. Engelmann and the late Henry Eggert. An attempt has 

 been made to give the distribution of the different species 

 over the various physiographic regions met with in an ideal 

 cross section of the Mississippi south of St, Louis. Under 

 each of these regions the various modifications have been in- 

 dicated by different numbers, the number being repeated 

 where the modification is analogous. Under a separate main 

 caption weeds have been listed, their distribution being ident- 

 ical on both sides of the river. Thus 1 indicates cultivated 

 fields, 2 the vicinity of dwellings, 3 pastures, 4 road;:.'ides, 

 5 roadside and railroad ditches, 6 creek banks, 7 hillsides, 8 

 hilltops, 9 limestone glades, 10 sinkholes, 11 ponds or lakes, 

 those lakes of the American Bottom which occur near the 

 bluff being indicated by 11, 12 prairies, the same number be- 

 ing used to indicate the bottom lands, 12 denoting the dry 

 bottoms, 13 thickets, 14 woods, 15 cliffs, 16 talus, 17 ravines, 

 18 railroad embankments, and the strip adjacent the tracks, 19 

 railroad cuts, 20 mud covered shores, 21 river islands, 22 mud- 

 flats, 23 sandy shores and 24 ballasted railroad tracks. By 



