26-20 Journal of Applied Microscopy 



LXX. Selagiiiella kraussiana (Kunze) A. Br. Krauss' Selaginella. 



Class and order, Selaginellales. Family, Selaginellaceae. 



This plant grows very luxuriantly in greenhouses and window gardens, if the 

 soil is provided with proper moisture. Suitable material may be had at any 

 time of the year. 



Sporophyte. 



1. Sketch an entire plant, showing branches, leaves, and roots. Note that 

 the branches occur only in one plane and that the roots are dichotomous. 

 Describe the character and arrangement of the leaves. How do you account 

 for the arrangement ? How does the plant accomplish vegetative propagation .'' 



2. Draw a leaf under low power. Under high power draw a single cell, 

 with chloroplast, from the lower surface. Draw also one of the stomata. 

 Where are the stomata situated ? Look for the ligule on the leaf. 



3. Cut cross sections of a fresh stem or of stems preserved in alcohol, mount, 

 and draw, representing the following structures : epidermis, cortical tissue in 

 which may appear sections of bundles passing to the leaves, two or more large 

 air spaces, and in the center of each space a vascular bundle. The bundle con- 

 sists of a central strand of xylem (wood) surrounded by a band of phloem which 

 is enclosed in a large-celled bundle sheath. Note the strands of cells passing 

 through the air space from the cortex to the vascular bundle. 



4. Draw one of the short bisporangiate cones (primitive flower) under dis- 

 secting microscope, showing microsporophylls above and one or more mega- 

 sporophylls below. 



5. Carefully pick ofif a microsporophyll and a megasporophyll each with its 

 sporangium, mount and draw under low power. Note the greater specialization 

 in the arrangement of the sporangia over that of Marsilea. Note the numerous 

 microspores in the microsporangium. How many spores in the megasporan- 

 gium ? 



6. Draw a microspore and a megaspore in exact proportion under low power. 

 How do you explain this dilTerence in size of the nonsexual spores? Determine 

 how many times greater in volume the megaspore is than the microspore. 



Gametophyte. 



7. From prepared slides draw the male and female gametophytes of Selagi- 

 nella, the archegonium, and antheridium, and the oosphere and spermatozoid. 



S. Make a diagram in the notes showing the life cycle of Selaginella. See 

 Fig. 12. 



9. Note. — It will be remembered that in the lowest archegoniates the game- 

 tophyte is the important plant in the life cycle, and that the sporophyte is very 

 small. Now in the highest forms the tables are turned and the sporophyte has 

 become the plant. Between such plants as Isoetes and Selaginella on the one 

 hand and the lowest living seed plants on the other, there is a considerable 

 hiatus, nevertheless it is not difficult to trace the transformation which was 

 necessary in passing from the condition of heterosporous pteridiophytes to the 

 lowest gymnosperms. 



