VARIATION 437 



* The accumulative action of changed conditions of life,'' sug- 

 gested by Darwin,* is consequently theoretically supported to 

 a certain extent by the theory of the continuity of the germ- 

 plasm : those determinants which varied in the first generation 

 continue to do so in a similar direction in the second and third. 



Professor Hoffmann has for many years been making very 

 interesting experiments in the Botanical Garden at Giessen 

 which bear on this point, some of which I will now describe. 



Various plants, bearing iiovvers of the normal structure, were 

 exposed during a number of generations to greatly modified 

 conditions of life ; they were, for example, grown crowded 

 together in small pots, so that each plant restricted the amount 

 of food obtainable by the others, and were thus scantily 

 nourished. Under this treatment some species — such as Nigella 

 damascena, Papaver alpinujii, and Tagetes patula — bore a 

 number of non-typical double flowers more or less frequently. 

 The fact that these deviations from the ordinary type in no case 

 appeared in the first generation, proves that they were due to an 

 influence exerted upon the germ-plasm, and not to the direct 

 influence of the abnormal conditions of nutrition upon the 

 soma of the plant. Seeds of normal wild flowering plants of 

 different species, when grown in cultivated soil or even when 

 thickly sown in pots, never produced plants possessing eveti 

 ojie double flower. Only in the course of several, and often 

 many generations, did any of these wild plants exhibit a greater 

 or less number of double flowers, or occasional modifications 

 in the leaves or in the colour of the flowers. It seems to 

 me that only one explanation can be given of this fact, viz., 

 that the altered conditions at first only produced imperceptible 

 variations in the germ-plasm of an individual plant, — such, 

 for instance, as alterations in the determinants for the leaves 

 or flowers in individual ids, but not in all of them at once. 

 These modified determinants were transmitted to the next 

 generation in consequence of the continuity of the germ- 

 plasm ; but since the causes of variation continued to operate, 

 the homologous determinants in several other ids also became 

 modified, and thus the number of modified determinants for 

 the leaves and flowers continued slowly to increase, until finally 

 they exceeded the normal determinants in number, and the 



* Darwin, 'Animals and Plants under Domestication,' Vol. II., p. 249. 



