1909] HILL— POLLINATION IN LIN ARIA 465 



shaded by the leaves of the trees and the taller plants of the forest 

 floor, those of the field or open places before the grass or other growth 

 overtops them. Their period of cleistogamy occurs when they are 

 not subject to the strongest light. The one exposed to the greatest 

 intensity of light, Viola pedata L., differs from most members of the 

 genus in not having such flowers. Its season of blooming as well 

 as environment correspond to those of L. canadensis when bearing 

 its largest flowers. As a perennial, the violet has the advantage 

 of drawing upon a supply of food stored in its much thickened root- 

 stock. When this is diminished or too much exhausted, it goes on 

 with the production of the enlarged summer-leaves, and by them 

 elaborates another supply of food for storage. This may be a good 

 explanation of its lack of the cleistogamy so general among its kindred, 

 since it does not seem adequate to the work of bearing flowers and 

 perfecting seed while producing the food for the future need of a 

 xerophytic perennial. Under diminished temperature and favorable 

 conditions of moisture its work of bearing petaliferous flowers may 

 be resumed in late summer and autumn, but they are mostly smaller 

 and much less developed than those of spring. V. lanccolata L. is 

 also a species frequent in our dune region. It is a light-loving plant, 

 often greatly exposed in the open sandy border of sloughs, but being 

 hygrophytic has a supply of moisture on which to draw. Hence 

 it passes its summer stage in the production of cleistogamous flowers, 

 which continues long after that of the petaliferous has ceased. Yet 

 it partakes of the general tendency among the violets, that of bearing 

 them on shorter, more hidden stems, with the additional habit of 

 producing them on stolens close to the ground. But L. canadensis, 

 being an annual subject to xerophytic conditions, cannot draw on 

 such resources as these two violets have. The development of its 

 cleistogamous flowers evidently depends on its relations to heat 



and moisture more than on those of light. 



V. DEGENERACY IN FLOWERS OF LINARIA 



In L. canadensis is found an example of a plant passing through 

 decadent stages to the condition of cleistogamy. The slight irregu- 

 laris of limb and the occasional remnant of a spur show degeneracy, 



arvin 



