CAPSELLA 165 



2. A stage in which the integuments are further developed, the outer 

 arising somewhat below the inner one. The large embryo sac is gener- 

 ally evident at this time in the center of the nucellus. 



3. A stage in which the outer integument has grown over and 

 beyond the inner one, so that only the extreme tip of the nucellus 

 is seen. At this time the ovule begins to bend over at its basal 

 region. 



4. Finally the outer and inner integuments grow completely over the 

 nucellus, almost meeting beyond to form the small opening called 

 the micropyle. Meantime the bending of the ovule brings the mlcro- 

 pyle close to the stalk of the ovule, so that the latter is therefore 

 completely bent on itself (campylotropous). This condition will be 

 found in the ovules of rather young, unopened flowers, and such 

 preparations may be cleared with potash. 



C. The development of the pollen tubes. Mount the pistil of an open flower 

 in water and examine the stigma under m.p. Note the papillce on its 

 surface, and among the papillss the germinating pollen grains, which 

 will be found sending tubes into the tissue of the stigma. Clear with 

 potash if too opaque. Draw. 



D. The development of the embryo. Remove the pistils from flowers, the 

 petals of which have begun to wither. Open the ovule case with a 

 needle and mount the ovules in a potash solution. The embryo may 

 sometimes be clearly seen'lying in the embryo sac. Press gently on the 

 cover glass and the embryo will be crushed or squeezed out. Note the 

 row of cells forming the siispensor, the lower one of which is much 

 enlarged. Make a number of preparations of younger and older 

 ovules, which are likely to show the following stages, and should be 

 drawn : 



1. The suspensor before the formation of the embryo, consisting of a 

 filament attached by a large basal cell near the micropylar end of 

 the embryo sac. 



2. The development of the embryo, beginning at the free end of the 

 suspensor, by the formation of walls in three planes, thus differen- 

 tiating a globular structure. 



3. The later growth of the embryo, with the appearance of two cotyle- 

 dons, and the development of the root at the point where the embryo 

 is attached to the suspensor. 



4. Lengthwise microtome sections of the ovules (Sec. 212) will show 

 the relation of the developing embryo to the enlarged and curved 

 embryo sac with its endosperm, and the integuments of the ovule 

 (see Principles, Pig. 309, H). 



