PINUS LARICIO 173 



the mature integument, referred to in K and L 

 (p. 170-171). The integument is analogous to an 

 indusium. Why? 



5. Underneath the testa, observe the thin, membran- 

 ous inner seed-coat, formed by a separation and 

 differentiation of an inner layer of the tissue of the in- 

 tegument. Describe its color and surface-character 

 as seen under the hand lens. Compare with Zamia. 



6. Observe the small hole through the micropylar end 

 of the inner coat. What does this represent? 



7. Remove the inner seed-coat, having care not to dis- 

 turb the brownish, membranous cap on the micro- 

 pylar end of the kernel. This cap is the remains 

 of the nucellus (megasporangium) . Note the modi- 

 fication of its tissue at the place through which the 

 pollen- tube passed on its way to the embryo-sac. 

 The remainder of the nucellus was consumed by 

 the female gametophyte during the development of 

 the latter. 



8. What is the homology of the white, fleshy kernel 

 of the pine seed. 



9. Make a drawing (X 4) of the endosperm and nu- 

 cellus. 



10. Remove the nucellar tissue. Is it firmly attached 

 to the endosperm? Describe the appearance of the 

 endosperm under the nucellar cap. 



11. Very cautiously separate the endosperm into longi- 

 tudinal halves. Begin the dissection at the end 

 opposite the micropylar end so as not to injure the 

 embryo-sporophyte within. 



12. Observe that the embryo lies in a distinct cavity or 

 chamber, its tissues being quite distinct, anatomic- 

 ally, from those of the gametophyte. Can you ac- 

 count for the formation of this cavity ? 



