Butters: seeds and seedling of caulophyllum. 13 



eral days later. Both integuments increase considerably in thick- 

 ness as a result of tangential cell division, so that in the ovules of 

 open flowers the outer integument is 200-300 mic. in thickness, and 

 the inner integument from one-fourth to one-third, as thick. Con- 

 siderable specialization of the cells of the integuments occurs before 

 the flowers open. The inner layer of cells of the inner integument 

 undergo frequent radial divisions. At the same time their proto- 

 plasm becomes more dense, so that they come to form a very dis- 

 tinct layer of columnar cells next to the remains of the nucellus, 

 and to such parts of the embryo-sac as are no longer covered by 

 the nucellus. A somewhat similar modification occurs in the inner 

 layer of cells of the outer integument, but the specialization of this 

 layer never becomes so well marked as in the case of the inner 

 integument. During the same period the stalk of the ovule increases 

 considerably in thickness, and a marked constriction is developed 

 between the stalk and the body of the ovule. 



The earlier stages in the development of the embryo-sac cannot 

 all be traced in the material at hand. Sections taken about twenty 

 da3^s before flowering show a cell about 20 mic. x 32 mic. — larger 

 than the adjacent nucellar cells, and with more vacuolar protoplasm. 

 The nucleus is in synapsis, and the cell is apparently the megaspore- 

 mother cell (Fig. i, PI, IV). The young embryo-sac increases rap- 

 idly in length, and the micropylar end increases also in width, 

 while the antipodal end becomes attenuated. Thus about ten days 

 before flowering the embryo-sac is a club-shaped structure, about 

 120 mic. long, 60 mic. wide at the micropylar end but with the antip- 

 odal one-third only 8 mic. wide. At this stage the embryo-sac com- 

 monly shows two or four nuclei, the antipodal nuclei being located at 

 the entrance to its narrow, antipodal portion. 



The growth of the embryo-sac is not associated with a corres- 

 ponding growth of the nucellus. The cells of the nucellus next to 

 the embryo-sac break down as the latter structure grows, and the 

 outer cells are pushed apart so that the distal end comes to form 

 a cap-like structure at the micropylar end of the embryo-sac (n Fig. 

 2, PI. IV). This structure persists until the seeds are almost mature. 

 A few cells at the proximal end of the nucellus remain as a sheath 

 about the narrow antipodal end of the embryo-sac (n Fig. 2, PL 

 IV). Between these portions of the nucellus the embryo-sac comes 

 into direct contact with the inner integument. 



