H 



MINNESOTA BOTANICAL STUDIES. 



The Mature Ovule. 



At the time of flowering the ovule is about i mm. long by .6 mm. 

 wide (exclusive of the stalk, which is about .3 mm. long by .4 mm. 

 wide). It has a somewhat rectangular oval outline. The nucellus 

 and the integuments are united in a broad and massive chalazal 

 region. A strand of vascular tissue extends up from the stalk. On 

 reaching the chalazal region this divides, and the xylem passes 

 over and around the chalazal region in two strands, while the phloem 

 spreads out laterally in a hood-like form and almost completely 

 covers the chalazal end of the ovule. (Text Fig. i, B & C). The 

 cells which lie between the vascular strands and the antipodal end 

 of the embryo-sac increase considerably in size, averaging about 

 twice as large as the other parenchyma cells of the integuments, 



B ■ ' C 



Text Figure i. Development of the ovule. A. Ovules in ovary five 

 weeks before flowering. X 100. B. Ovule ten days before flowering. X 40. 

 C. Ovule at flowering time. X 40. 0, outer integument, ;', inner integument, 

 Mj n, nucellus, e, embryo-sac, v, vascular bundle, ph, phloem, spreading out 

 from bundle in chalazal region of ovule. The xylem strand is double in this 

 region. 



and become somewhat vesicular. This group of cells later gives 

 place to the peculiar cavity found in the chalazal region of the 

 maturing seeds. 



The cavity of the outer integument is oval with the narrow end 

 towards the micropyle. The outer part of the latter structure is a 

 tubular canal 4 mic. in diameter and about 300 mic. long, the inner 



