124 PRACTICAL BOTANY 



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. 



II. 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 specimens up to the almost 

 mature fruit: treat them as before described (p. 119), 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 division 

 so as to fill the cavity of the embryo-sac with endosperm which 

 embeds the embryo. 



7. The great increase in size of the embryo-sac, and of the 

 whole ovule. 



8. Note also the changes in the integuments, and the dis- 

 appearance of the nucellus as the ovules become mature. 



On looking over a number of such sections, numerous cases 

 of division of nuclei, illustrating various stages of the process, 

 may be found. These points may be very well studied in the 

 embryo-sacs of Fritillaria impcrialis, &c. 



III. The continuity of protoplasm through cell-walls has been 

 shown in the sieve-tubes (p. 71). Similar observations of fine 

 threads of protoplasm traversing the cell-walls may be made in 

 the endosperm of various seeds, and these are merely prominent 

 examples of a widespread phenomenon. 



