ENDOSPERM 213 



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 disappearance 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 

 imperialis, &c. 



II. For obtaining preparations of the embryo in situ, 

 and of the endosperm surrounding it, the ovary of 

 species of Potamogeton will be found to be good material : 

 it should be previously hardened in spirit. 



Cut longitudinal sections of a single carpel, parallel 

 to the flattened sides. Mount in glycerine, and examine 

 with a low power. One of the sections will probably 

 be found to include 



1. The embryo-sac, in which are contained 



2. The embryo, with a very short suspensor, the 

 basal cell of which is greatly enlarged. 



3. The endosperm, a tissue which lines the embryo- 

 sac, and varies in appearance according to the stage of 

 development of the ovary. 



III. The continuity of protoplasm through cell- walls 

 has been shown in the sieve-tubes (p. 115). 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 

 wide-spread phenomenon. 



