1910.] Forms of Plants as a Result of Environment. 557" 



formation of stamens into petals is particularly striking. As far as we know, 

 it does not occur in the Sempervivum of nature, while it is very frequent in. 

 the altered flowers. 



This rapid sketch of my experiments with Sempervivum, of which the 

 results are verified with other species, will show you, as I hope, what a 

 decisive influence environment has on the development and form of a 

 flowering plant. The forms to be observed in nature correspond to the 

 conditions. Only by quantitative alterations and new combinations of the 

 common factors can we recognise the inexhaustible richness of the potentialities 

 lying in the specific inner structure of the cells. 



Our scientific task consists in determining as exactly as possible the part 

 played by all external factors, and (what is far more difficult) in examining 

 the internal alterations, the results of which are the appearance of a definite 

 form. This physiology of development and form is a new branch of modern 

 biology, investigated by botany and zoology at the same time. 



During my explanation you will probably have asked yourselves what 

 connection such results have with the question of the transformation of 

 species. The immortal work of Charles Darwin has had a far-reaching 

 influence on all branches of biology, and has also given a fruitful impulse to 

 the physiology of development. But to avoid disappointments and mis- 

 understandings, we must bear in mind that the study of the alterations of 

 plants described by me has nothing to do directly with the question, and is 

 also wholly independent of any theory. We start from the fact, verified 

 times without number, that every species has a constant innate structure, of 

 which the reactions and variations depend on certain factors. All the 

 alterations of the Sempervivum take place only under definite conditions 

 and are replaced by others under different conditions. 



A hereditary transmission of these alterations is improbable in the 

 highest degree, and has never been observed. But the question arises 

 whether it is perhaps possible through particular effects of environment 

 to cause internal changes which are transmissible to the descendants. 

 From horticultural experience we know of the appearance of some hereditary 

 modifications, called by De Vries " mutations." We observe, for instance, 

 anjong the individuals of a red flowex'ing race (genus), one which shows at 

 once and in all its offspring white flowers. We can cause the formation of 

 white flowers by high temperature and feeble light as with Sempervivum. 

 But this alteration is oidy a simple variation which disappears again under 

 ordinary conditions, while the white flowering plant, created as a mutation, 

 preserves its character e\"crywhere. 



How such mutations, so important for horticulture, are produced is wholly 



