1909] HILL— POLLINATION IN LIN ARIA 461 



pressure to which they are subjected, the flowers are poorly developed, 

 but otherwise show nothing peculiar in their structure. The corolla 

 is crumpled and deformed, but "preserves even its natural color, 

 with the two brown spots on its upper lip." The calyx alone loses 

 its color. Fructification takes place regularly. Michalet adds that 

 the phenomenon can be produced at will by heaping earth around 

 the lower part of the plant, this not interrupting the flowering of 

 the covered portion. The treading of cattle and the pressure of 

 wheels bring about the same result. As this plant of Europe and 

 northern Africa is now introduced into this country, being, according 

 to Gray's New manual, "occasional on ballast or waste grounds," 

 an opportunity is provided for observing its behavior here. Another 

 species of north Africa, L. agglutinans Pomel. var. lutea, belongs to 

 this class of hypogeous plants, as observed by L. Trabut in Algiers. 

 It has cleistogamous flowers on shoots which spring from the stem 

 near its base and ripen their fruit underground. 14 



III. RELATIVE ADVANTAGES OF THE TWO MODES 



It is a distinct advantage to a plant growing under the conditions 

 of Linaria canadensis to prolong its period of fruiting with a lessened 

 demand on its supply of food. The environment is xerophytic. 

 At Oregon it was the southern slope of a steep hill, fully exposed 

 to the light and heat of the sun. The soil was sandy, and soon parted 

 with any moisture that was supplied by rains and dews. The con- 

 ditions in the dunes are similar, the slopes of sand hills or along paths 

 and roadways in open sunny spots. The growth is usually scattered, 

 though many plants may form a community, but the ground is not 

 covered with a dense mat or bed as it commonly is by L. vulgaris. The 

 slender stems provide but meager shade for the ground about their 

 roots. In the early part of the season, or if it continues wet, the 

 radical shoots form rosettes around the base of the stems, which 

 protect the roots to some extent. In ordinary seasons these soon 

 wither, and they may not be formed at all on plants which spring up 

 later, being minute or wanting as in the smaller early plants. It is also 

 a species poorly adapted to competition. When pressed by perennials, 

 or by plants disposed to form a close stand, it soon disappears. And 



J 4 Knuth, Handbuch der Bliitenbiologie 32:113. I 9°5- 



