296 THE JOUllNAL OF BOTAT^Y 



Cax ax Allogamous Pla:n^t be Hoimozygous ? 



Species originate from crosses : so thought Linne, and several Men- 

 delists seem to cherish the same idea. Nevertheless, many of the 

 hybrids have become homozygous. Beyond doubt some of the 

 allogamous groups are able to develop in the same direction as the 

 self-impregnating forms really do. 



Many new forms are unlit for free competition. That concerns 

 not only sterility and other inlirmity. My experience with the strains 

 of Gapsella was very significant. Imported species are seldom able to 

 compete with natives. I will cite an example. At Vestervik, onl}"" 

 200 km. distant from the capital, most of the strains from Stockholm 

 disappear in a short time. I know exceptions from the rule, especially 

 strains from Mediterranean countries. Thus Nature makes a great 

 difference even between very similar competing units. This rule 

 prevails among many groups of plants. 



By crosses the weak hybri Is will, of course, disappear. But also 

 many vigorous new combinations will be excluded hy the force of 

 Darwin's law, not being able to keep the field in the environment. 

 If a strain have collected by degrees the best qualities for the 

 struggle for life, it will easily surpass other combinations and develop, 

 I think, in direction to be homozygous. If homozygous, it has the 

 greatest chance to resist in the struggle, because it tends to keep its 

 good qualities. I suppose that Nature in this way creates new 

 constant units. 



Nature axd its Analysts. 



I do not know whether the successors of Mendel have met with 

 greater difiiculties in their studies than Linne and his successors have 

 done. It would need immense work to discover all the natural units 

 and groups of the organic world. It requires acute observation to 

 discover the diiference between variation ex loco and constant varie- 

 ties, to prove the constancy, to discern the collective species, and to 

 discover and prove the existence of plant hybiids. This work has 

 proceeded but two centuries, and is not nearly complete in our day. 



Science begins by stating and arranging the facts ; it continues 

 with anal3^sis. Linne discovered and proved the immutable characters 

 of the constant varieties and species. Mendel and his successors dis- 

 solved the characters and found fixed and immutable genes. Linne 

 speaks of three different categories of existing varieties ; Johannsen 

 divides the variability into three kinds of variation. These three 

 categories of Linne and Johannsen are, of course, not identical : the 

 second category is widely different, and according to Linne contains 

 only constant varieties. I think we need in science categories both 

 of existing organisms and of their variability, generally both the 

 Nature fact and its analysis. In other branches of the science the 

 same rule prevails — no one can construct meteorological facts from 

 ]>hysical laws, nor the laws of epidemics from a bacteriological 

 laboratory. 



