130 PRACTICAL BOTANY. 



(b) One Integument several layers of cells thick, 

 united with the funiculus, and covering the body of the 

 ovule completely, excepting a narrow channel (Micro- 

 pyle) near the apex of the ovule. Within this lies 



(c) The Nucellus, a mass of cellular tissue in which 

 is embedded 



(d) The Embryo-sac (Macrospore), a large oval 

 cell, situated 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. 



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

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

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

 Oosphere) 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. 



Note the Tapetum, consisting of cells more or less 

 disorganised, which partially or completely surround the 

 embryo-sac. 



If similar sections be cut from buds of Helleborus fmtidus 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 a second integument being present in these cases, the structure 

 of the ovule will appear to correspond to that of ffelleboms. 



