12 MINNESOTA BOTANICAL STUDIES. 



tigial pericarp. The gynaeceum of the flower consists of a single 

 carpel enclosing two large, erect, anatropous ovules. These stand 

 side by side in the ovary, with their micropyles turned away from 

 each other. Even in the bud the edges of the carpel are in loose 

 contact, and the cavity of the ovary is in communication with the ex- 

 terior by a very narrow slit which opens upon the stigmatic surface 

 of the pistil. After flowering the carpel undergoes very little growth. 

 In less than two weeks the developing seeds push it open, and 

 are entirely exposed, the carpel remaining as a small bract-like struc- 

 ture at the base of the seeds. 



Development of the Ovule. 



The ovule shows no marked peculiarities in its development. It has 

 from the beginning a long and massive stalk ( 150 mic.x 180 mic.) . The 

 nucellus is formed at the distal end of this. In the youngest ovules 

 sectioned (about a month before the opening of the flowers) the 

 nucellus appears as an almost hemispherical mound of tissue directed 

 obliquely upwards at the distal end of the ovule. At this stage 

 the primordium of the inner integimient appears as a collar-like 

 ridge encircling the nucellus, and scarcely protruding above the 

 general surface of the ovule, while the only trace of the primordium 

 of the outer integument is a slight convexity of the tissues at the 

 distal end of the ovule opposite to the nucellus (Text figure i, A). 

 The nucellar mound grows rapidly in height becoming first hemi- 

 spherical and then elliptical in outline. At the same time the unequal 

 growth of the distal portion of the stalk causes the axis to bend 

 rapidly, turning the nucellus into first a lateral and finally an in- 

 verted position. During this bending of the axis, the outer integu- 

 ment appears first as an outgrowth from the summit of the bending 

 stalk, and then, as it develops farther down the sides of the stalk, 

 as a hood-like covering about the nucellus. From the beginning it 

 is much more massive than the inner integument, and when it has 

 once begun to develop it grows more rapidly than the latter. 



About twenty days before flowering (Fig. i, PI. IV), both integ- 

 uments are about one-half the length of the nucellus. The inner 

 integument is two or three cells in thickness, the outer, about twice 

 as thick. Thereafter the outer integument is the longer. It com- 

 pletely covers the nucellus at least ten days before the flowers open, 

 while the inner integument closes over the top of the nucellus sev- 



