114 BLASTOGENIC VAEIATIONS. 



cells, and still more from the union of fresh and over- 

 ripe germ-cells." Upon plants, as far as I am aware, 

 no direct experiments have been made, but some obser- 

 vations of De Vries * upon (Enothera Lamarckiana 

 bear closely upon the matter. Some seeds of this plant 

 had been kept for 5J years before sowing, and it was 

 then found that only about 1 per cent, of them germi- 

 nated, instead of the usual 14 per cent, or so. Of the 

 seedlings obtained, however, about 40 per cent, were 

 " mutations," whilst the proportion of mutations ob- 

 tained from fresh seeds was only 1 to 5 per cent. 



Weismann's second factor in the production of varia- 

 tions is the so-called amphimixis, or sexual reproduction 

 in multicellular organisms, and conjugation in unicel- 

 lular. That this is one of the chief causes of variation 

 was maintained by W. K. Brooks f some years ago. 

 Basing his theory on Darwin's hypothesis of Pan- 

 genesis, he considered that as every " gemmule " of the 

 spermatozoon united with that particle of the ovum 

 which is destined to give rise in the offspring to the cell 

 which corresponds to the one which produced the germ 

 or gemmule, then such a cell will be a hybrid, and will 

 therefore tend to vary. In his opinion the egg-cell is 

 the conservative principle which controls the transmis- 

 sion of purely racial or specific characters, whereas the 

 sperm cell is the progressive element which causes 

 variation. 



To what extent are we justified in assuming that this 

 process of amphimixis does furnish an inexhaustible 



* Die Mutationstheorie," p. 360. 



f " The Law of Heredity: A Study of the Cause of Variation and 

 the Origin of Living Organisms," Baltimore, 1883. 



