108 THE BRACKEN -FERN. 



arising apparently from the notch at the forward end 

 of the gametophyte. 



The following materials should be collected: the un- 

 derground stem or rhizome with the roots that grow 

 from it, care being taken not to tear away the fine roots; 

 a piece of young rhizome suitable for sections, the latter, 

 and a good supply of roots with their tips uninjured, 

 being preserved in formalin or alcohol and a few young 

 roots preserved for microtome sectioning; a supply of 

 leaves, with and without sporangia, some being pressed, 

 some being preserved in alcohol or formalin, and some 

 pieces of leaves bearing sporangia being prepared for 

 sectioning; a supply of ripe sporangia with their spores, 

 preserved dry. 



About six weeks before the laboratory work is to be 

 begun some of the spores should be sown on damp earth 

 or sand in a dish that should be kept covered. This sow- 

 ing will usually furnish a supply of gametophytes for lab- 

 oratory study. 



Pteris cretica and P. cristata, common greenhouse ferns, 

 will serve well for this work, as will also the maiden- 

 hair fern, Adiantum pedatum. Numerous other ferns 

 will furnish excellent material in case none of the above 

 can be obtained. 



GENERAL STRUCTURE. 



I. THE RHIZOME AND ROOTS. Observe: 



1. The flattened dorsi ventral stem, the upper and lower por- 

 tions being divided by prominent ridges. 



2. The roots arising from the ventral surface and sides. 



3. The roots, each (if uninjured ) with a small root-cap at its 

 tip. 



