134 TYPE STUDIES 



Illustrate in a habit sketch the characteristic features 

 of frond and stem, and draw in detail a portion of a 

 fruiting frond, showing the venation and distribution of 

 sporangia. 



B. The sporangia. Scrape off some of the sporangia from a 

 sorus and mount in water. Draw under h.p. a side view of 

 a sporangium from which the spores have been discharged. 

 Note and show in the figure : 



1. ThB stalk. 



2. The flattened spore case consisting of thin-walled tissue 

 except for a row of thick-walled cells along the margin, 

 forming the ring (annulus). Note the extent of the ring 

 and the position of the thickened portions of its walls. 



3. The wide rent in old and empty sporangia opposite 

 the ring. 



4. Spores free or inclosed in the sporangia. Draw in detail. 



5. Soak some ripe, unopened sporangia in water and place 

 on a slide without a cover glass. Watch them under 

 l.p. as they become dry. Explain from the movements 

 of the ring how the sporangium opens and discharges 

 its spores. 



The fact that the fern plant has no sexual organs but produces 

 instead asexual spores, and that it alternates with a sexual genera- 

 tion (as will appear later), makes it a sporophyte. The details of 

 spore formation show that the spores are comparable to those of 

 the bryophytes. 



6. The details of the development of the sporangia and of spore forma- 

 tion can best be studied from microtome sections through the sori. 

 Species of Aspidium are especially favorable for this study (Sec. 212). 

 Follow stages as outlined in Goebel, 16, Pig. 165. Note that the spores, 

 sixty-four in number, are developed in groups of fours, tetrads, in 

 spore mother cells. 



C. The cell structure, or histology, of the stem. The fern is 

 not a favorable subject for a detailed study of the tissues 

 characteristic of higher plants, but certain peculiarities are 

 important. 



