FERN CROSSING AND HYBRIDISING. 289 
germinate in such close juxtaposition as to cause more or less overlapping 
when the prothalli develop, and obviously we thus produce conditions 
favourable to cross-fertilisation, especially if at the proper time, that is 
just before the prothalli are full size, we produce a small inundation, 
A A+B B 
Fic. 107.—LastTREA DILATATA LEPIpDoTA (A) x L. p. cristata (B) 
L. D. Leprpota-cristaTa (A+B) STANSFIELD. 
either by immersing the pan until the water percolates through the soil, 
and just submerges the undersides of the prothalli, or by watering 
overhead, which is less to be commended. My own idea of the best 
way is that the pan should be placed in warm water, say about 
U 
