312 METHODS IN PLANT HISTOLOGY 



nous tissue. From the underground bud, cut off the fertile portion of 

 the leaf and fix it separately. The reduction divisions in the spore 

 mother-cell take place soon after the leaf appears above ground. The 

 later sporogenous stages and the reduction stages furnish excellent 

 illustrations of the "tapetal plasmodium." 



For all stages in sporangia, until they begin to turn brown, use the 

 Chicago chromo-acetic-osmic solution. Stain in safranin, gentian vio- 

 let, orange, for morphological study; and in iron-alum haematoxylin 

 with a light tinge of orange for mitotic figures. 



Fig. 101. — Cyrtomium falcatum: various stage.s in the development of sporangia, covered by a 

 peltate indusium. Chromo-acetic-osmic; safranin, gentian violet, orange. X90. From Chamber- 

 lain's Elements of Plant Science (McGraw-Hill Book Co., New York). 



Prothallia. — The best prothallia are those found growing naturally. 

 In Sphagnimi bogs and on damp shaded banks, and on rotting logs, 

 they are sometimes found in abundance, and may be so large that 

 they look like Pellia. It is easier to find them in the ferneries of green- 

 houses on pots and on the benches. 



Prothallia are easily grown from spores. Ripe spores of some fern 

 or other can be obtained at any time of the year either in the field or in 

 the greenhouse. Spores usually germinate promptly and produce good 

 prothallia, even if the sowing is not made for several months after the 

 spores have been collected. 



Fine prothallia of Pteris aquilina have been grown two years after 

 the spores were gathered. Some, however, must be sown at once, or 

 they will not germinate at all. Spores which are large and contain 

 enough chlorophyll to make them appear greenish should be sown at 

 once. The spores of the common Osmunda regalis, and of the other 



