HOW TO GROW PROTHALLIA. 363 



in water in a saucer, or upon a flower-pot or flower-pot saucer 

 similarly kept constantly moist. In a room it may be covered 

 over with a bell-globe. In this way all the early stages of de- 

 velopment can be well obtained, and it needs only to scrape off 

 some of the germinating spores day by day with the blade of 

 a pocket-knife, and lay them in water on an object-slide, to be 

 able to follow the development. For full-grown prothallia for 

 section-cutting, the spores can be well sown on a bed of cocoa- 

 nut fibre refuse, flattened down in a large flower-pot saucer, with 

 a hole in the bottom, or a seed-pan, and well drained, kept moist 

 until towards the time they are needed for examination. Over- 

 head watering, if needed, can be given with a spray such as is 

 used for diffusing scent, and by gardeners for the purpose of 

 spraying foliage with insecticides. Another highly-recommended 

 method is to sow the spores upon a slab of peat which has been 

 first boiled in water in order to kill any seeds or spores it may 

 contain, and then soaked with the culture fluid recommended 

 for the cultivation of Spirogyra. The spores are then sown, 

 and the turf covered with a bell-glass and placed in a north 

 window. With a favourable temperature germination begins 

 in from three to five days. With care to keep them moist, 

 the spores can likewise be germinated upon a glass-slide, and, 

 with the very careful addition of minute quantities of culture 

 fluid, can be grown to some size, though their growth thus is 

 usually much more slow. Owing to their large size, the spores 

 of Ceratopteris lend themselves pretty readily to this mode of 

 culture, which enables easy observation under the microscope, 

 and facilitates also the fixing and permanent preservation of 

 specimens showing the early stages of germination and prothallial 

 development. The spores of Ceratopteris can likewise be germi- 

 nated by sowing upon a nutrient fluid, and preserving a moist 

 atmosphere. Floating prothallia are then developed, with rhizoids 

 and sexual structures in their normal position, but submerged. 

 The spores of various kinds of Gymnoqramtne (widely grown as 

 " silver " and " gold " ferns) are also exceedingly good for growing 

 prothallia. With young prothallia spermatozoids can be very 

 well studied in suspended drops in moist chambers, and the nature 

 and duration of their movement, and the changes accompanying 

 it, readily followed. 



Reproduction of Eqnisetum. The sporangiferous axis of Eqni- 

 setum arises in the form of a cone, at the tip either of the ordinary 



