Theory of Plant Breeding 



Weissmann's followers do explain such cases by 

 assuming that these practisings and trainings affect the 

 germ-cells and so may alter the organism. But amongst 

 botanists there has been, from the first, much scepticism 

 about germ-plasmas. Such cases as the following are 

 very difficult to explain if there is any truth in Weiss- 

 mann's theory.* 



When leaves of begonia are cut off and placed in 

 soil, they take root and may form new plants which 

 flower and fruit. 



There are no germ-cells in those leaves, only ordinary 

 protoplasm, so that, as Professor Henslow pointed out 

 (early in the controversy), there is no use in botany for 

 a theory of germ-plasmas as distinguished from ordinary 

 protoplasm, which indeed is quite mysterious and com- 

 plex enough for all theoretical purposes. 



The theory of mutation, which owes its origin to De 

 Vries, is still the subject of an active and vigorous con- 

 troversy in the botany of to-day. 



It is based on the peculiarities of certain seedlings 

 of Oenothera Lamarckiana which De Vries discovered 

 growing wild at Hilversum in Holland. 2 



Now this species was described by Lamarck from 

 certain specimens growing in the Paris Botanical Garden, 

 and which were supposed to have come from America, 

 The wild plant, if it does still grow in America, has not 

 been found of late years. On the other hand, it has 

 been alleged that it is not a species at all but merely a 

 hybrid. If this is true, it is difficult to put any faith in 

 those mutants. Even if it were a wild American species, 

 it has experienced two distinct changes in climate (to 

 Paris and thence to Holland), so that its variations could 



* The excellent account of Weissmannism in Thomson's "Heredity " 

 should be consulted for further details, and indeed for the whole theory of 

 modern evolution. 



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