FERN GROWING 65 



five varieties, the sixth character being obtained from the germ. 

 In the latter case two of these cells did not germinate. 

 Judging of the case from the doctrine of probability, more than 

 one sperm must have landed in one or more of the female 

 cells, because almost the same number of spores from the 

 eight varieties were sown together. Now, if only five of the 

 varieties had deposited sperms (one in each cell), the chances 

 against this would be 1 20 to i ; if six, this would be increased 

 to 720 to I ; and if we take into consideration the whole of 

 the eight varieties, it would be 40,320 to i. We are there- 

 fore strengthened in the conclusion that it is requisite for a 

 number of sperms to impregnate each cell. 



In a series of experiments, using a mixture of equal 

 amounts of spores of four distinct varieties, the result has 

 invariably been alike, viz., that in a large number of seedlings 

 only one or two are found to show the characters of the four 

 parents, an increased though still a small number, of three 

 out of the four parents, and the remainder only combinations 

 of two. In these experiments no single individual was like 

 any one of the varieties that had been sown together. If only 

 a single sperm impregnated a cell, we should have a number 

 of plants in which the sperm had impregnated a cell on its 

 own prothallus, and in not a single instance has this occurred. 

 Another reason for the conclusion that more than one sperm 

 had impregnated the cell is the fact that, where we have 

 obtained plants showing the four varieties, we still do not 

 raise two alike, and this seems to affirm that the variation is 

 caused by a percentage of the sperms of any one variety 

 predominating. 



Amongst the objectors to multiple parentage Mr. G. B. 

 Wollaston considered that only a cross between two varieties 

 could be obtained, and that the other peculiarities were the 

 result of a previous cross. Professor Vines and others con- 

 sidered that the experiments should be made with plants 



