PTERIDOPHYTES— EQUISETALES 



303 



loam and sand, smoothed and pressed down until a hard surface was 

 obtained. This was flooded and allowed to stand until the water 

 soaked into the soil. Then spores were sown, the flat was covered with 

 glass and placed in a sunny room of the greenhouse. No more water 

 may be needed until the plants are 1 mm. high. Water with potassium 

 permanganate if there is any tendency to damp off. 



Fig. 95. — -Equisetum prothallia: A-C, Equisetum arvense: C shows two antheridia. D-H, E. 

 telmaieia; H shows six antheridia. After Walker. X30. 



The prothallia fix well in chromo-acetic acid. The younger stages 

 may be stained in iron-alum haematoxylin and mounted in Venetian 

 turpentine. The older stages, even of E. arvense, are too large for such 

 mounts. E. laevigatum has prothallia a centimeter in diameter. 



For the development of antheridia, the blepharoplast, and the de- 

 velopment of the sperm, fix in the Chicago chromo-acetic-osmic solu- 

 tion and stain in iron-alum haematoxylin. For oogenesis, and sperma- 

 togenesis, especially the centrosome situation, the sections should not 

 be thicker than 3 /x. The sperm of Equisetum is the largest in Pterido- 

 phytes. 



