No. 577] MUTATION THEORY OF BE VRIES V 



regarded as a species in the strict sense, while those of 

 the type of Rosa blanda, in which abortive pollen similar 

 to that characteristic of forms clearly recognized as hy- 

 brids, is present, are hidden hybrids. It follows that in 

 Rosa (or practically any of the other rosaceous genera 

 cited above), there are three types of individuals, namely 

 good species, hidden hybrids and open hybrids. The 

 middle condition is extremely common among the Angio- 

 sperms and is of the greatest importance in connection 

 with clear views in regard to the origin of species. Obvi- 

 ously constant or relatively constant hybrids can not rank 

 with pure species, such as are characteristic for example 

 of the Gymnosperms, in discussions in regard to the 

 origin of species by mutation or otherwise. The conduct 

 of such forms is conditioned to a greater or less extent by 

 their mixed blood. We may appropriately designate obvi- 

 ous hybrids as phenhybrids and those hybrids which are 

 recognizable as such by their internal morphological char- 

 acters as crypthybrids. Crypthybrids will probably when 

 studied more extensively in cultures by the geneticist, give 

 evidence of their hybrid origin in cultures. There can 

 be no doubt that many of the recognized species of the 

 Angiosperms are in reality crypthybrids. The enormous 

 multiplication of species in this great group of plants is 

 in all probability largely related to hybrid crossing. It 

 is of the utmost importance however to keep clearly in 

 mind that such hybrid species or crypthybrids are not at 

 all in the position of true species from the evolutionary 

 standpoint and that conclusions derived from their study 

 can not be applied without large reserves, to the question 

 of the origin of species in the strict sense. The species of 

 Pinus, so far as we have any evidence, since the main 

 types are known to have existed well back into the Meso- 

 zoic, in all probability illustrate the origin of species some- 

 what along the lines of the Darwinian hypothesis. On the 

 other hand the species of Rosa present obviously an 

 entirely different problem in evolution and the necessity 

 of making distinctions if we are to reach any definite bio- 



