186 KANSAS UNIVERSITY SCIENCE BULLETIN. 



The action of the wind on plants is partly direct by tensile 

 stresses and partly indirect by increasing transpiration; both 

 these actions are the more energetic the taller the plants or the 

 higher their location. 



Where my Townsendias occurred the soil is a loose, cal- 

 careous deposit, allowing the water quickly to percolate 

 through it. 



When the character of its habitat is considered, it would be 

 expected that the anatomy of Townsendia must be that of a 

 xerophyte. 



TOWNSENDIA EXSCAPA. 



Townsendia exscapa is perennial from a woody taproot 

 which averages ten centimeters long and three to four milli- 

 meters in diameter at the thickest portion. The stem grows 

 from one to four inches high. The fact that this plant is low 

 helps it to endure the strong winds prevailing in its locality. 



The character of the stem varies in different plants. In 

 some, while young, it is quite simple, bearing only a few heads 

 of flowers ; in others it is several-branched, bearing six or more 

 heads. As a rule, however, it gradually becomes more and 

 more branched with age until the whole plant may attain a 

 breadth of ten to twelve inches, bearing about 100 heads of 

 flowers. The leaves are all clustered at the base, narrowly 

 linear or slightly spatulate, and one to two inches long. The 

 flowers are white and are borne in sessile heads one to one and 

 one-half inches broad. In figure 2 is shown a photograph of 

 Townsendia. When the flowers of the larger plants have gone 

 to seed the plants have the appearance seen in figure 3. 



In the discussion of the histology of Townsendia the stem 

 will be first treated, then the root, and last the leaf, and the 

 different tissue systems under each will be examined. 

 The Stem. 



Tegumentary Tissues. — The protection of the mature stem 

 is provided for by a cutinized epidermis and cork tissue. All 

 the walls of the epidermis are cutinized. In figure 4 is shown 

 a small portion of the cutinized epidermis. In the following 

 table is given the average thickness of the walls of the epi- 

 dermal cells and the average length and width of the cavity of 



