138 A PINE. 



2. The parts composing each stamen, the short stalk (the 

 filament), the two long sporangia that make up almost the 

 entire body, and the flat extension at the outer part. Tear 

 open a few sporangia, and study the microspores (pollen- 

 grains), observing: 



3. The central cell from the wall of which two lateral blad- 

 dery outgrowths, the "wings," have developed. 



4. Within the central cell the granular cytoplasm and usually 

 one or two nuclei. 1 



5. Draw a microspore. 



6. Observe the structure of a small piece of the sporan- 

 gium wall and make a sketch showing it. 



IV. THE MEGASPOROPHYLL. 3 



From a one-year-old cone remove some of the sporophylls 

 and observe: 



1. On each sporophyll one or two elevations on its upper 

 side near the axil, between it and the axis of the cone. 

 These are the megasporangia, or ovules. 



2. The open end of the ovule extending downward. 



3. By means of prepared longitudinal sections of the ovule 

 cut perpendicular to the flat surface of the carpel, study 

 the structure of the ovule, observing the following parts: 

 a. The outer covering (the integument) extending down- 

 ward about the opening. 



1 If there are two nuclei, it is evident that the microspore has begun 

 to germinate to produce the male gametophyte and male cells. Often 

 one of the new cells formed through division of the spore nucleus will 

 be seen to be a lenticular one rather closely pressed against one side 

 of the microspore wall. The nucleus of the other cell may lie anywhere 

 in the larger mass of cytoplasm. 



J The material most needed will be found in cones collected at the 

 time they are about a year old. If there is at hand a good supply of 

 entire cones and separate sporophylls collected at intervals of ten days 

 or two weeks during spring, so that they are suitable for sectioning 

 to show different stages of development, microtome sections should 

 be prepared. See Chamberlain's "Methods in Plant Histology," pp. 

 119-121. 



