160 SCOTCH PINE. 



including about the middle third of the ovule. Mount all 

 the sections, and treat with potash. Examine with a low 

 power, and note 



h. The /#/-$ of the ovule : integument, nucellus and 



micropyle. 



/*. The parts of the scale : the scale proper and the 

 wing of the seed. Notice that the tissues of the 

 scale are continuous with those of the wing and 

 ovule ; a faint trace of the coming lines of separa- 

 tion may however be detected. 



/ The differentiation of the tissues of the scale into 

 two kinds : the one of densely packed small cells 

 forming an outer layer with deeper seated fibers ; 

 the other of looser larger cells, forming the inter- 

 mediate portion. 



k. The differentiation of the integument of the ovule 

 into two layers, the outer of densely packed small 

 cells, the inner of looser larger cells. 

 /. The discoloration of the apex of the nucellus. 

 /;/. The presence of a large cavity in the nucellus, the 

 embryo-sac, filled with a delicate transparent tissue, 

 endosperm. 

 Examine with a high power, and note 



n. That the body of the nucellus is almost entirely 



displaced by endosperm cells. 



o. The wall of the embryo-sac ; wavy and usually 

 broken away from the remaining cells of the 

 nucellus in cutting the section. 

 /. The endosperm cells; observe 

 i. The delicacy of the walls. 

 ii. The contents ; thready protoplasm and a very 



large round nucleus with a nucleolus. 

 iii. Draw a few endosperm cells. 



