PTERIDOPHYTES—FILICALES 
261 
Various species of Pteris are common in greenhouses and are very- 
good for development of sporangia. Any fern of the Aspidium 
type will yield a good series, and some, like Cyrtomium, may show a 
fine series in a single sorus. Marattia, which is likely to be found in 
botanical gardens, will illustrate the “synangium” type; Angiopteris 
has a sporangium which forms an easy transition to that of the 
Cycadales. 
For the development of a typical sporangium of the eusporangiate 
type, nothing is better than Botrychium. Buds of B. virginianum 
taken in September or October show sporangia with well-marked 
sporogenous tissue. For a study of the development of sporangia, 
cut off the fertile portion and fix it separately, using chromo-acetic 
acid with 5 or 6 drops of 1 per cent osmic acid to 100 c.c. of the solu¬ 
tion. Stain in iron-alum haematoxylin. The reduction divisions in 
the spore mother-cell take place after the leaf arrives above the surface. 
The Prothallia.— Prothallia can usually be found on the pots in 
the ferneries of greenhouses. Ripe spores of some fern or other can 
be obtained at any greenhouse at any time in the year, and spores 
of most of our native ferns germinate well and produce good prothallia, 
even if the sowing is not made for several months after the spores 
have been gathered. 
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 members of the genus, must be sown as soon as ripe, or 
they fail to germinate. The prothallia of 0. regalis } if carefully 
covered with glass, may be kept for a long time, and they become 
quite large. Prothallia of this fern in the writer’s laboratory pro¬ 
duced ribbon-like outgrowths 5 mm. wide and more than 5 cm. in 
length. These prothallia continued to produce archegonia, anther- 
idia, and ribbon-like outgrowths for more than a year, when they 
suddenly “ damped off.” Lang watered prothallia with a weak 
solution of permanganate of potash, which kills the fungi but does 
not injure the prothallia. He does not state the strength of the 
solution, but 4 or 5 crystals to 1 liter of water seems to be effective. 
The prothallia of most ferns will grow for a long time under such 
conditions. Pteris aquilina and many other ferns often furnish a 
