232 Methods in Plant Histology 



3 mm. long and 1 or 2 mm. thick. Near large plants, look for small 

 sporelings, not more than 1 or 2 cm. in height. Dig very carefully 

 and you may find the gametophytes attached. The soil should be 

 examined for smaller specimens. Most of the gametophytes will be 

 found at a depth of 1 to 3 cm. Fix in chromo-acetic acid. 



No one has yet succeeded in raising the prothallia from the spores. 

 The prothallia always contain an endophytic fungus, supposed to be 

 Pythium, but even when this is present the spores do not germinate. 



Ophioglossum. Although widely distributed, our only common 

 species, Ophioglossum vulgatum, is so poorly represented in individuals 

 that it may be regarded as a rather rare plant. The stem is erect 

 and subterranean, as in Botrychium, but is smaller and easier to cut. 

 The sporangia are in an unbranched spike and even the early spo- 

 rogenous stages appear after the leaf is above ground, so that it is 

 comparatively easy to get material if you know where it grows. 



No one has succeeded in finding prothallia in the United States. 

 Bruchmann, who studied the Lycopodium prothallia, also found 

 and studied the prothallia of Ophioglossum vulgatum. The prothal- 

 lium is circular in transverse section, about 1 mm. in diameter and 

 sometimes more than a centimeter in length. It is subterranean 

 and looks like a small, irregular rootlet. No one has been able to 

 raise prothallia from spores. 



Prothallia of some of the tropical and south temperate species 

 are easier to find, and early stages have been grown from spores. 



