FERNS. 167 



prothallium look for conic projections, the archegonia (see fig. 139) ; among 

 the rhizoids look for smaller but more numerous, rounded projections, the 

 antheridia. Compare the prothallium with the thallus of marchantia. 

 Sketch a prothallium under the low power of the microscope if there is time. 

 Among the prothallia search for some showing the young fern plant. 



Demonstration 4O. 



273. To show the structure of the sexual organs of ferns. Make thin 

 sections lengthwise of the prothallium along the middle line. These are 

 best made in collodion or paraffin, and mounted in balsam. If the teacher 

 has not the apparatus for making them, prepared slides may be purchased 

 for the demonstration. Let the pupils sketch the structure of an antheridium 

 and archegonium (see paragraphs 281 and 282), and name the parts. 



If there is time and material the teacher may demonstrate young pro- 

 thallia soon after the germination of the spores. 



The following description of the sexual stage of ferns is for 

 reading and study. 



For further studies on the gametophyte phase of ferns, see 

 the author's larger " Elementary Botany," Chapter XXVI. 



274. Sexual stage of ferns. We now wish to see what the 

 sexual stage of the ferns is like. Judging from what we have 

 found to take place in the liverworts and mosses we would infer 

 that the form of the plant which bears the sexual organs is 

 developed from the spores. This is true, and if we should 

 examine old decaying logs, or decaying wood in damp places in 

 the near vicinity of ferns, we would probably find tiny, green, 

 thin, heart-shaped growths, lying close to the substratum. 

 These are also found quite frequently on the soil of pots in 

 plant conservatories where ferns are grown. Gardeners also in 

 conservatories usually sow fern spores to raise new fern plants, 

 and usually one can find these heart-shaped growths on the sur- 

 face ot the soil where they have sown the spores. We may call 

 the gardener to our aid in finding them in conservatories, or 

 even in growing them for us if we cannot find them outside. 

 In some cases they may be grown in an ordinary room by keep- 

 ing the surfaces where they are growing moist, and the air also 

 moist, by placing a glass bell jar over them. 



