132 STUDY or COMMON PLANTS. 



IV. Using material that has been kept in alcohol, mount 

 some of the sporangia in water as before, and examine 

 microscopically. Run a drop of glycerine under the cover 

 glass and notice the result. Repeat the experiment until 

 you are satisfied as to the way the spores are discharged 

 from the sporangium. 



Note. — This is by no means an easy problem. Notice where the 

 sporangium ruptures, the form of the cells composing the annulus, and 

 the changes they undergo with its change of position. Try the use of 

 different media, such as strong salt solution, etc. Compare the sporangia 

 of different ferns, and see whether all have the same structure and behave 

 aUke. 



V. Under the highest power, study the form and struct- 

 ure of the spores. Draw one or more of them. 



VI. Taking almost any sorus except the oldest ones, 

 study the development of the sporangium by carefully 

 comparing the structure at different ages. A series of 

 drawings should be made illustrating as many stages as 

 possible .1 



Prothallium. 



If fern spores are sown on soil, or on pieces of decayed 

 wood, and are kept in a moist atmosphere, they will germi- 

 nate, and give rise to a structure known as the prothallium. 



I. The early stages of development of the prothallium 

 are easily observed by examining the spores at intervals 

 during the first few days after they have been sown. 

 Microscopic examination shows that the spore swells, the 

 outer coat, exospore, ruptures, and the inner coat, endospore, 

 protrudes in the form of a papilla, which rapidly elongates 

 into a delicate, tube-like structure, the first root-hair. The 



1 Cf. Goebel, Outlines of Classification and Special Morphology, p. 217 

 et seq. 



