202 MORPHOLOGY AND LIFE HISTORY 



cell forms four microspores (young pollen- 

 grains). They thus arise in tetrads. 

 Using slides showing pollen-grains, observe: 

 (m) The more advanced disorganization of the 

 tapetal-cells, including the breaking down of 

 their cell-walls, and the fragmentation of their 

 nuclei into two or more. These cells serve 

 to nourish the spore-mother-cells. 

 () The microspores. Do they lie free or con- 

 nected? Describe their shape, surface-features, 

 and number of nuclei. 



(0) State again the first stage in the germination 

 of the microspore. What is the resulting 

 structure? What is its homology? 

 5. Megasporangia; megaspore-mother-cell. 



Using prepared slides showing the megaspore- 

 mother-cell, observe: 



(a) The outline of the ovary as seen in cross-section. 



(b) The presence or absence of an epidermis; 

 of stomata. 



(c) The "cells" of the ovary, each containing, in 

 the section, 



(d) Two young ovules (megasporangia). Are the 

 ovules straight or curved? 



At this stage the tissue of the ovule is chiefly 

 nucellus, but soon there develops at the base 

 of the ovule, outside of the nucellus, 



(e) The inner integument, which grows up around 

 the nucellus, leaving at the summit only a 

 small passage, 



(/) The micropyle. Outside the inner integument 



there usually develops 

 (g) An outer integument. In anatropous ovules 



the development of the outer integument 



