2 Trans. Acad. Sci. of St. Louis. 



probably others germinate in the fall, producing rosettes which 

 live over winter. Arctium, Cnicus, Lactuca Canadensis and 

 L. Floridana are mesophytes growing in shaded places or 

 wastes. The others are prairie xerophytes. 



The perennials may be divided into three series ; those 

 which form crowns, those which propagate by stems, those 

 which propagate by adventitious buds upon roots. 



Crown formers. Under this head are included plants which 

 have no well marked adaptation for vegetative propagation, 

 but in which the base of the stem or stems lives through the 

 winter. The new shoots are produced from buds upon the 

 base of these stems. Sometimes the crown is short and com- 

 pact upon a well-marked tap-root. 



This is well illustrated by Kuhnia eupatorioides, Lepachys 

 columnaris, and our four species of Lialris {L. punctata, L. 

 scariosa, L. squarrosa, L. pr/cnostac/iT/a). In such cases it 

 is difficult to tell whether the buds are axillary or adventitious. 

 Those mentioned are all xerophytes. In the first two ex- 

 amples the root is long and slender. In Liatris it forms a 

 peculiar woody corm-like body. The structure of this root is 

 interesting as showing its adaptation to xerophilous condi- 

 tions. In L. punctata the outer part of the root is protected 

 by a layer of cork several cells thick. The bulk of the interior 

 is made up of parenchyma cells well stored with water. This 

 water can be easily forced from a cut root with a little pres- 

 sure even in the driest weather. The outer region of the 

 root is well supplied with strands of sclerenchyma fibers. 

 These strands lie in radial rows continuous in xylem and 

 phloem. In cross-section they are circular or oblong (in a 

 radial direction), and are separated from each other by wide 

 cushions of parenchyma cells. In the xylem there is a com- 

 paratively thin strand of pitted vessels lying along the inner 

 side of the sclerenchyma strand. These strands of mechan- 

 ical tissue become thinner and farther apart towards the center 

 until they disappear and the whole interior of the root is 

 made up of the water tissue. Maceration with Schulze's 

 solution shows the sclerenchyma fibers to be comparatively 

 short, pointed and often branched at the ends, with numerous 

 nearly straight canals radiating from the very thin cell cavity. 



