172 MORPHOLOGY AND LIFE HISTORY 



7. After making a longitudinal incision, very carefully 

 remove the nucellus, noting the greater thickness of 

 the tissue at the micropylar end. This tissue serves 

 as nourishment for the germinating pollen-grain. 



8. Within the nucellus is the globular young female 

 gametophyte, or endosperm. Describe and (from 

 your reading in the text-book) account for its 

 consistency. 



9. With the razor make a median, longitudinal section 

 of the entire ovule. Study and draw, naming all 

 the parts. 



/. Older Stages in the Development of the Ovule: 



1. Examine ovules collected about April i, as directed 

 under /. Compare their size with that of the 

 younger ovules. Observe the fleshy texture being 

 assumed by the outer portion of the tissue of the 

 integument, and the differentiation of a harder 

 inner layer (endopleura). 



2. Describe the changes which the nucellus has under- 

 gone. Account for these changes. (The appear- 

 ance of the nucellar tissue may be due, in part, to 

 its disintegration by the growing pollen- tubes.) 



3. Remove the nucellus and describe the appearance 

 of the endosperm. Note the slight depression in 

 its micropylar end. What change has taken place 

 in its consistency? Account for the change. 



4. With a scalpel cut away the endopleura, and then, 

 with a razor, make a clean, median longitudinal 

 section of the endosperm, and observe, imbedded 

 in its micropylar end, two or more archegonia. 

 These open into the depression, mentioned above, by 

 a short neck, composed of only two cells. The short 

 neck-canal may be seen if the section passes through 

 a suitable plane. 



