A MANUAL OF BOTANY 141 



spore number in a fern plant ? Wliy is such a plenitude 

 of spores produced? What would you judge is produced 

 when a spore from the sporangium germinates? 



Sterile leaves and sporophylls. Examine sterile leaves 

 (not having sori) of ferns like the sensitive, ostrich, or 

 cinnamon. Observe the absence of the sori, so common in 

 other fern leaves. Examine now the peculiarly contracted 

 brownish or greenish clustered structures borne on stalks, 

 and found growing from the same underground stems as 

 the naked or sterile leaves you have just looked at. Crush 

 a single division of one of these; mount and examine (/j)), 

 and observe the similarity to the sporangia studied before. 

 These contracted stalk structures are strangely modified 

 leaves called sporophylls, bearing nothing but sporangia. 



The G-ametophyte 



Where found. The spores of the sporangia, when ger- 

 minating, produce small, inconspicuous plants known as 

 gametophytes or prothalli. The green coating on the ground 

 of a fern house is largely composed of these minute stages 

 in the fern life history, which, with the fern plants (com- 

 monly so called), consisting of leaf and rhizome, constitute 

 the alternation of generations of the fern. 



Structure. Examine a gametophyte (yip), and observe 

 its color and form. What features remind you of the land 

 liverworts? Observe the cell structure. Discover on the 

 lower surface, near the notch, oblong cells, archegonia, and, 

 near the opposite end, more or less mixed with rhizoids, the 

 antheridia. What is the actual size of the gametophyte? 



Drawings. Make the following drawings: 



1. A complete sporophyte (leaf and rhizome). 



2. Details of venation (??i or Ij^). 



3. A cross section of a fern rhizome to show the various 



tissues {Ip), 



