LABORATORY STUDIES 265 



and examine it, using a low power. Note the sac-shaped spore 

 cases upon the under side of the leaf. Mount some of the spores 

 dry, using no cover-glass, and examine with the 16 mm. 

 objective. Breathe upon the spores very gently to moisten 

 them, and notice the coiling of the elaters; observe the quick 

 uncoiling which takes place upon the evaporation of the 

 moisture. 



(c) Sow a quantity of the fresh spores upon moist earth or 

 porous pottery, covering with a bell-jar and taking every pre- 

 caution to secure constant moisture. The spores wiU begin to 

 germinate in a few days, when studies of successive stages of 

 growth may be taken up. By care the mature gametophytes 

 (prothallia) may be grown, and the antherids and archegones 

 studied. 



(d) Make very thin cross-sections of the stem of the Common 

 Horsetail. Note the position of the vascular bundles. Now 

 make a vertical section of the bundles and study the tissues, 

 using high powers. 



(e) Study the breathing-pores on the green stems of the Com- 

 mon Horsetail. Compare these with those of the Scouring 

 Rush. Study also the disposition of the chlorophyll-bearing 

 tissue in cross-sections of both stems. 



(/) Examine underground stems of HorsetaUs, and compare 

 the structure with that of the aerial stems. Make cross-sec- 

 tions of the roots which are attached to these underground 

 stems. 



LITERATURE OF CALAMOPHYTA 



The same as for the preceding phylum, and 

 M. C. Stopes, Ancient Plants, London, 1910. 



