PTERIDOPHYTES— FILICALES 



315 



further wetting is necessary, except to take care that the water in the 

 pan does not dry up. With Pteris longifolia there may be antheridia 

 in 2 weeks ; archegonia in 3 or 4 weeks ; and in 5 or 6 weeks, abundant 

 sporophytes in various stages. Prothalha grown by Costello's method 

 are entirely free from soil and, consequently, very convenient for 

 cutting or for mounting whole. 



While there should always be a study from living material, it is 

 worth while to make permanent mounts, even for habit study. For such 

 study, the prothallia should be mounted whole. Fix in the Chicago 



Fig. 104. — Fern prothallia: A-C, Pteris longifolia, bearing antheridia at an early stage; X230. 

 D-F, Nepltroflium molle: D, mitasis in the antheridium; E, young sperm mother-cell and parts of 

 6 others, 3 of them showing the blepharoplast from which the cilia will develop; F, antheridium with 

 nearly mature sperms. D-F X 580. 



chromo-acetic-osmic solution. If the material shows any tendency to 

 break up, use 2 c.c. of acetic acid instead of 3 c.c. In cities where water 

 is treated with copper or other substances, the difficulty may some- 

 times be due to the water rather than to any excess of acetic acid. 

 Formalin-acetic acid (10 c.c. formahn, 5 c.c. acetic acid to 100 c.c. 

 water) is good for material which is to be mounted whole. Stain some 

 in iron-alum haematoxylin, and some in phloxine and anilin blue. 

 Mount in Venetian turpentine, using material from each stain for 

 each mount. Select stages so that each preparation will show the fila- 

 mentous stage, the apical cell stage, the group of initials stage, and 

 also antheridia and archegonia. 



