THE HEREDITY OF ACQUIRED CHARACTERS IN PLANTS. 77 



THE HEREDITY OF ACQUIRED CHARACTERS IN 

 PLANTS. 



By Rev. Professor G. Henslow, M.A., V.M.H., &c. 



When Darwin propounded his theory of Evolution, or " the origin of 

 species by means of natural selection," he assumed two things as axioms, 

 viz. variability, i.e. the power in plants and animals to vary, and the 

 heredity of acquired variations. 



He was not so much concerned with the causes of variations in 

 animals and plants ; but, given the variations, natural selection would, he 

 maintained, decide which was the best fitted to survive in the struggle 

 for life. That changed external conditions of life are somehow the 

 primary cause of variations is admitted by all ; and we must look to the 

 living Protoplasm, together with its nucleus, as the instruments in 

 organisms, which can be affected and excited by external influences, to 

 set up new variations in their structure, such being acquired characters. 



These consist of any changes in the outward form or internal anatomy 

 of structures, as well as the "habit"* of a plant induced by external 

 agencies. 



With regard to heredity Darwin's words are : " The correct way of 

 viewing the whole subject would be to look at the inheritance of any 

 character whatever as the rule, and non-inheritance as the anomaly." f 

 Elsewhere he says : " Natural selection will be enabled to act on and 

 modify organic beings at any age, by the accumulation of variations 

 profitable at that age, and by their inheritance at a corresponding age." t 



Dr. Weismann, however, introduced the word soma (i.e. " body ") for 

 the vegetative organs of plants, viz. roots, stems, leaves, and the external 

 organs of the flower would be included ; but, on the other hand, he 

 distinguished an imaginary "germ-plasm " § in the reproductive organs, 

 such as the embryo-sac, as distinct from the general protoplasm or living 

 substance everywhere else within all living cells of the plant's soma. 



It was this hypothetical substance to which alone he attributed, by 

 means of its continuity, the power of carrying on all hereditary charac- 

 teristics in the offspring. 



When his attention was called by botanists to the fact that certain 

 plants, such as Begonias and Mosses, are very generally propagated by 

 means of fragments of their leaves &c, i.e. his "soma," he supposed that 

 some portions of the germ-plasm must have been diffused with the proto- 

 plasm in such cases. 



Since, however, the propagation of plants by their vegetative organs 

 of any kind is possible and frequently done, both in nature and artificially, 



* By " habit," it is usually meant that the duration of life, e.g. whether annual, 

 biennial, or perennial, or a dwarf size, a procumbent position, &c, is characteristic, 

 f Origin of Species, 6th ed. p. 10. J Ibid. p. 67. 



§ I am not here concerned with Weismann's theory of its immortality. 



