2624 Journal of Applied Microscopy 



4. Tangential section. Draw under low power, showing part of the xylem 

 with tracheids and cross sections of the medullary rays. 



5. Under high power draw part of a tracheid from radial section, showing 

 the peculiar bordered pits. 



6. Sketch part of a polished section of an old pine stem, showing bark, 

 cambium, sap wood, heart wood, and pith. Notice the medullary rays. Notice 

 also that each annual ring of wood is double — spring wood and fall wood. On 

 which side is the spring wood .'' Describe the growth of a pine tree in height 

 and thickness. 



(d) Sporophylh of Pi ii us laricio. 



Use fresh or alcoholic material. 



1. Draw a staminate (microsporangiate) cone under dissecting microscope. 

 Describe the arrangement of the stamens (microsporophylls). 



2. Draw a stamen under low power, showing the outer (under) side with 

 two microsporangia (pollen sacs). How different from the microsporophyll of 

 Selaginella in structure and function ? 



3. Draw a young carpellate (megasporangiate) cone under dissecting micro- 

 scope. Describe. Note that the parts are smaller at the lower end. 



4. Draw a carpel (megasporophyll) from the lower side under low power, 

 showing the bract (true leaf blade of the carpel) and the large ovuliferous scale. 

 This may be an outward growth of the chalazal region of the ovules. Draw the 

 carpel from the inner (upper) side, showing the two ovules (megasporangia) 

 and the ovuliferous scale. Compare the carpel with the megasporophyll of 

 Selaginella. 



5. Draw a mature carpellate cone. Note the spiral arrangement and that 

 the carpels at the base are undeveloped and contain no seed. This is an exam- 

 ple of rudimentary organs. Be careful to distinguish rudimentary organs (rudi- 

 ments) from incipient organs (incepts) and from nascent organs. 



(3. Note. — ^The staminate and carpellate cones of the pine represent pr mi- 

 tive flowers. Are these flowers monosporangiate (one kind of spores in the 

 flower) or bisporangiate (both kinds of spores in the same flower) ? Compare 

 with the cone in Selaginella. Is the pine tree (sporophyte) moncEcious or 

 dioecious ? 



(e) Carpellate Cone of Larix decidua. 



Collect carpellate cones of the usual type and some which have the tip con- 

 tinued as a leafy branch. Preserve in alcohol. 



1. Sketch a normal cone in which terminal growth has been completely 

 checked. 



2. Sketch a cone on which a leafy branch has developed at the outer end. 

 Note the gradual transition from carpels to ordinary foliage leaves. Sketch a 

 number under dissecting microscope, showing this transition. This continued 

 growth or prolongation of the floral axis of the larch cone is a good example of 

 reversion to a more primitive condition or atavism. Compare with the ordinary 

 ferns, Lycopodium lucidulum. and Cycas. 



