170 



to the north of these localities, and it may be looked for with confidence in the 

 northern portions of the State. 



Prenanthes aipera Michx. As reported, this species is confined to Jefferson 

 and Clark counties. There is reason to believe it of more general distribution. 



Lactuca hirsuta Muhl., L. Floridana Gaertn. and L. cucophcea Gray, are all 

 confined to the southern counties, Monroe being the extreme northern reference 

 in any case. 



Only one form appears to be strictly western in its State distribution. 



Solidago Missouriensis Xutt. This species is reported from Jasper county by 

 Prof. Barnes, but with this exception is confined to counties bordering the Wabash 

 River as far south as Gibson and Posey. 



It is thus seen that 36 species have a single reported station ; that 8 species 

 are strictly northern, 24 species southern and 1 species western in distribution 

 within our territory. The range of many of these 69 species will doubtless be ex- 

 tended as the result of further study. The remaining 144 species of the family 

 are so generally reported, or are reported from such widely separate stations as to 

 make it probable that they are found throughout the State in greater or less 

 abundance. In many cases the distribution of these general forms is so thor- 

 oughly worked out as to give with a fair degree of certainty the determining fac- 

 tors in the distribution. It is impossible in this paper to give in detail illustrative 

 cases. In a general way, water courses may be said to be an important determin- 

 ing factor. In the case of Liatris pycnostachya Michx., a prairie form, the south- 

 ward extension of the species from the prairie region is found to follow closely 

 the course of the Wabash River as far south as Gibson and Posey counties. The 

 same thing is true in a less marked degree of Eupatorium sessilifolium L., which 

 nowhere wanders far from water ways. 



The prevailing winds play a large part in the direction of movement of com- 

 posite species. After lodgment has once been obtained, the direction in which 

 any given form spreads seems in many cases to be absolutely conditioned by the 

 direction of the prevailing winds at the season of the dissemination of the 

 achenes. A number of lines of distribution are easily attributable to this con- 

 ditioning factor. 



The great trunk lines of railway may serve to introduce new forms, many may 

 find lodgment because of impure seed supplies furnished the agriculturists, but 

 the after distribution, with but few exceptions, is determined by water courses and 

 prevailing winds. 



To a slight degree within our area the elevation seems to determine distribu- 

 tion. Thus our extreme southwestern counties are but 300 feet above sea level. 



