PINUS 189 



chamber, its tissues being quite distinct, anatomic- 

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

 count for the formation of this cavity? 



13. Note that the embryo is composed of a main axis, 

 bearing a whorl of cotyledons borne near one end. 

 Can you detect distinct regions of the axis? If so, 

 how many, and how are they distinguished? How 

 many cotyledons are there? Is the number always 

 either odd or even? 



14. Observe that the embryo is attached at the end 

 opposite the cotyledons to a slender filament, the 

 suspensor. At this end of the embryo-chamber 

 may frequently be seen the disorganized remains of 

 other embryos that failed to develop. In rare 

 instances two embryos develop in one seed. This 

 is called polyembryony, a condition very common 

 in lemons, and other citrous fruits. 



15. Make a drawing of the young sporophyte, 50 mm. 

 long. 



1 6. Make a median longitudinal section of the embryo, 

 and observe that the portion of the axis below the 

 cotyledons (hypocotyl) is encased in an outer, 

 strongly developed root-cap, which completely en- 

 closes the hypocotyl. Note further that the coty- 

 ledons are borne on the hypocotyl. From its op- 

 posite end (radicle-end) the tap-root will develop. 

 The hypocotyl is the first internode of the sporo- 

 phyte. Where is the first node? 



17. At the summit of the axis, above the cotyledons and 

 surrounded by them, observe the conical epicotyl. 

 It will develop into the second and subsequent 

 internodes. Explain the meaning of the term 

 epicotyl. 



1 8. Construct three diagrams (X 5) showing (a) the 



