242 PLANT-BREEDING 



gamopetalous flowers occur in the mallows and in the hya- 

 cinths, symmetrical corollas and decussate leaves are spread 

 over the families of the natural system in the most capricious 

 manner, and even the forms and structures of the leaves do 

 not show any relation to systematic affinity. Assuming the 

 same causes for the same phenomena, the physiologist is 

 led to the conclusion, that the visible characters must be the 

 result of internal properties which may be the same in widely 

 different groups of plants. These internal qualities may 

 pass from species to species by the laws of inheritance or be 

 produced anew in distant famihes and genera. 



The chemist tries to connect the visible properties of his 

 substances with the assumed qualities of molecules and atoms, 

 and to explain, by this theory, their conformities and their 

 divergencies. In the same way, the physiologist explains the 

 likenesses and the differences of his plants, by the assump- 

 tion of equally invisible units, which are supposed to under- 

 lie the visible phenomena. These units he calls unit-char- 

 acters. For him they are the resting pole in the ever-mov- 

 ing tide of the outward forms. On this principle he tries 

 to explain the common features of plants, independently of 

 the question whether they are closely related or belong to 

 distant groups. It is a wide field for observations and induc- 

 tions, but the study heightens our appreciation of the real 

 nature of all living beings. It is a kind of biological analy- 

 sis, leading to a knowledge of the intimate elements of which 

 the plants are built up. 



The study of these elements or unit-characters has led 

 to the discovery of a most significant phenomenon. It is the 

 regular coincidence of marks, which hitherto had been re- 

 garded as quite independent from one another. This asso- 

 ciation has been shown to obey natural laws, and the study 

 of these laws enables us to predict one mark from the obser- 

 vation of the other. The relation of the color and form of 



