MALE FERN. 351 



soon be covered by the spores set free by the bursting of the 

 sporangia. 



Get some flower-pots or shallow seed-pans, some lumps of peat or 

 leaf-mould, and some glass sheets or bell-jars. If you use flower- 

 pots, half fill the pot with gravel and then put in enough peat to fill 

 the pot to an inch from the top ; if seed-pans are used, simply stand 

 the lump of peat in the middle of the pan. The vessels and soil can 

 be sterilised either by baking them in a hot oven for a few hours, or 

 by steeping them in boiling water ; if you bake the soil afterwards, 

 moisten it and the pot or pan. 



Shake some spores over the soil, and cover with the glass ; the 

 latter keeps the soil moist, since the evaporated water condenses 

 and runs back into the vessel, but the glass should be removed now 

 and then to renew the air. Set the vessels out of direct sunlight ; 

 the early germination of the spores is hastened by gentle warmth. 



Another method is to sow the spores on previously heated or 

 scalded bits of brick or tile sloping into water in a dish, instead of 

 using soil. Do not sow the spores too thickly, and do not water 

 them from above. 



In a few weeks you will see greenish threads creeping over the 

 soil, with here and there a small green disk. After a month or two, 

 you may see a few small leaves appearing on the prothalli. If the 

 prothalli are thickly crowded, thin them out, as one does with seed- 

 lings. 



493. Development of the Pern Prothallus. For the early 

 stages in germination of the spore, pick up, with needle or knife- 

 point, soil on which spores have been sown, as soon as young pro- 

 thalli can be seen ; or place spores in a hanging drop of water or 

 Knop solution in a moist chamber. 



Note (1) the bursting of the thick outer spore-coat ; (2) the out- 

 growth of the spore-contents, covered by the inner coat, to form a 

 short green filament ; (3) the early formation of a colourless un- 

 divided rhizoid from the base of the green thread ; (4) the formation 

 of transverse walls in the elongating green thread, giving rise to a 

 row of cells ; (5) the setting-in of oblique walls at the free tip of the 

 thread, forming a two-sided or wedge-shaped apical cell from which 

 segments are cut off right and left ; (6) the more rapid growth of 

 the tissue at either side of the apical cell, causing the latter to 

 occupy a notch and the prothallus to become heart-shaped ; (7) the 

 formation of further rhizoids from the underside of the young pro- 

 thallus. 



494. General Characters of Prothallus. Note the 

 naked-eye features of a large well- grown prothallus its 

 flattened form, its kidney- or heart-like outline, its green 

 colour, and its size (generally about a quarter of an inch 

 in diameter) ; the smooth upper side, with the notch at the 



