FERN GROWING 73 



this plant. Impregnation of a single germ by a single sperm 

 would give us a proportion of plants like the seed-bearer for 

 a lengthened period, instead of losing the true species in two 

 or three years when not isolated. 



If this new fact, owing to insurmountable difficulties, has 

 not been seen by miscroscopical examination, the experiments 

 have demonstrated it mathematically ; for, if we get the 

 combination of four varieties at once, it must prove that a 

 single combination of any two of these could not produce 

 this result : a + /3 could only form a^, not a^yS. The mixture 

 of blue and yellow can only be green. 



DETAILS OF EXPERIMENTS. 



Altogether, in the forty years, more than nine hundred 

 experimental sowings of spores have been made, and from 

 these the following have been selected as illustrations of more 

 than ordinary interesting results. 



These experiments increased gradually ; they were few 

 at first, but increased enormously when the fact of multiple 

 parentage gained credence. In one year they exceeded a 

 hundred, and from 18S7 to 1892 nearly five hundred different 

 combinations of mixed spores were being carefully watched. 



Occasionally the spores have either not germinated or 

 have been afterwards destroyed either by confervoid growth 

 or by want or excess of water. Altogether this destruction 

 has been on a very limited scale. Dr. Fox was several times 

 extremely unlucky, even to failing with the whole sowings of 

 a year. 



By always sowing each combination in three or more 

 pans, and using different soils, there is not much chance of 

 failure. Germination varies materially as regards time on 

 different soils ; it is quickest on the damp loam of a reversed 



