The Origin of Species 345 



perature, and nutritive conditions, he showed that 

 not only the habit of the plant might be greatly 

 changed but the color and size of the flower, and 

 sometimes even the number of different parts, might 

 be altered very much ; so that in the case of a species 

 of house-leek (Sempervivum), for example, the 

 differences in the flowers were much greater than 

 those between some of the species of the genus. 



Klebs' conclusions from his studies are that varia- 

 bility and inheritance are the results of physiological 

 changes entirely and there is no necessity for as- 

 suming the existence of definite formative structures 

 or protoplasmic units, pangenes, or determinants, 

 etc. Unfortunately the possibility of hereditary 

 transmission of the changes induced by environ- 

 mental conditions, has not yet been investigated as 

 fully as could be wished. 



CONCLUSION 



No Single Theory Satisfactorily Explains All the 

 Facts of Evolution. From a study of the behavior 

 of plants in a state of nature, as well as under ex- 

 perimental conditions, it is certain that no one of 

 the many theories that have been advanced can 

 explain satisfactorily all of the phenomena asso- 

 ciated with the evolution of the vegetable kingdom. 

 There is no question that mutations or discon- 

 tinuous variations do occur, and that these may be 

 the beginning of new species is exceedingly proba- 



