162 CARROLL— ON DEVELOPMENT OF 



the hypodermal layer, which is composed of greatly enlarged cells, 

 begins to take on the thickening characteristic of the endothecium. 

 Adjacent to the connective this enlargement of cells and development 

 of thickenings may involve two or three layers of cells. The epidermal 

 cells become somewhat swollen and vesicular. Toward the point of 

 rupture these epidermal cells disappear, and toward the connective 

 they increase to two layers. It is the tension set up between these two 

 tissues which apparently accounts for the rupture. After dehiscence, 

 the epidermal cells appear as shrunken remnants adherent to the outer 

 wall of the endothecium. If not too old these epidermal cells after 

 dehiscence still show a tendency to swell up. Apparently the loss of 

 turgor and collapse of the epidermal cell releases the tension of the 

 endothecium and dehiscence occurs. Loew (30a) (discussed briefly in 

 Engler and Prantl (49) has described the mechanism of dehiscence in 

 7. Roylei, Walp. About the time of origin of the endothecium, pairs 

 of pollen chambers of neighboring stamens become joined to form one 

 cavity, through breaking down of intervening walls. A similar appear- 

 ance occurs in I. fulva, but there is no breaking down of walls between 

 stamens, but rather a dehiscence of the external pollen sacs in the 

 lower part of the anther toward each other. In I. Roylei, according to 

 Loew, through a drying of the epidermal cells the anther walls press 

 into the pollen chamber and force the pollen upward as a column. 

 Dehiscence in fulva occurs longitudinally down the inner face. Usually 

 dehiscence takes place before the opening of the flower, so that when 

 the sepals and petals of the unopened flower are separated the interior 

 is found to contain abundant discharged pollen. Similar early dehiscence 

 occurs in other species (Knuth 26). Several hours to a day after the 

 opening of the flower the whole whorl of stamens becomes detached 

 together and falls from the flower. As the whorl falls it generally 

 carries with it much good pollen. In experiments with self-polhnation 

 noted above on I. fulva, pallida and sultani the pollen from the fallen 

 anthers was used to pollinate the stigma with entire success. Bennett* 

 states that he never found that the stamens fell away spontaneously, 

 but that the whole flower fell carrying the still concealed pistil with it. 

 This conduct of the plant in England seems to have been an abnormahty, 

 perhaps induced by a somewhat cold, moist, unfavorable climate in a 

 foreign home. In America the petals and sepals persist for several 

 hours or a day after the fall of the stamens; flowers bearing pistil but 

 no stamens are normal in fulva and pallida and in sultani in the green- 

 house. 



