212 PRACTICAL BOTANY 



B. DEVELOPMENT OF THE ENDOSPERM. 



I. This may be traced in the embryo-sac of Caltha 

 palustris in material which has been fixed and pre- 

 served in absolute alcohol or strong methylated spirit : 

 it is an advantage to collect the material on a hot 

 day, and place it in alcohol without delay; by this 

 means many nuclei may be fixed in various stages of 

 division. 



Cut transverse sections of the carpels of a flower of 

 Caltha palustris which is full blown, or even beginning 

 to fade, and also sections of successively older speci- 

 mens up to the almost mature fruit : treat them as 

 before described (p. 204), and compare them : they may 

 illustrate the changes which appear in the embryo-sac 

 subsequently to fertilization, viz. : 



1. The penetration of the micropyle and apex of the 

 nucellus by the pollen-tube. 



2. The first stages of development of the embryo, 

 which in this case remains relatively small, the seed 

 being an albuminous one ; the embryo will thus be 

 seen in situ. 



3. The division of the central nucleus of the embryo- 

 sac into two, subsequently into four, eight, &c. 



4. The disposition of the nuclei, as they increase in 

 number, as a dense series embedded in the protoplasmic 

 film at the periphery of the embryo-sac. 



5. The formation of cell-walls between these nuclei, 

 so that the embryo-sac is lined internally by a single 

 layer of cells of the endosperm. 



6. The ingrowth of these cells, and their subsequent 



