206 PRACTICAL BOTANY 



situated centrally a short distance below the apex of 

 the nucellus. 



Examine the embryo-sac with a high power, and 

 observe 



1. The granular, vacuolated protoplasm which fills it : 

 embedded in this are to be found 



2. A large central nucleus, with highly refractive 

 nucleolus. 



3. At the micropylar end of the embryo-sac, three 

 cells, with clearly defined nuclei. Two of these (the 

 synergidae) fill the apex of the sac, the third (the 

 ovum) being placed laterally, a little below the apex. 



4. At the posterior end of the sac are three cells 

 (the antipodal cells), also with clearly defined nuclei. 

 Divisions of these cells occasionally occur, so that their 

 number may be found to be greater than three. 



. t Note the tapetum, consisting of cells more or less 

 disorganized, which partially or completely surround the 

 embryo-sac. 



If similar sections be cut from buds of Caltha palustris of 

 various ages, and be treated in the same way, the development of 

 the ovule, and more especially of the embryo-sac, may be followed, 

 and the various stages of it may be observed. 



Make similar sections of the ovary of species of Lilium, or 

 Yucca, and compare them with the above. With the exception 

 of certain minor points, the structure of the ovule will appear to 

 correspond to that of Caltha. 



FERTILIZATION. 



I. Remove from flowers of Stellaria media, which have 

 just faded, the three styles: moisten them with alcohol, 

 and mount quickly in water: note the cylindrical 



