1906] Brainerd, Hybridism in the Genus Viola, — II 7 



somewhat limited district of Austria, and remarks on the "most 

 extraordinary tendency of the forms to hybridize; in no other genus 

 does there appear such a multitude of hybrids as among the violets." 

 Our blue stemless violets are all distinct from those of Europe, but 

 the disposition to hybridize seems to manifest itself in all groups of 

 the genus, and on both Continents. 



Laws relating to known Hybrids among Flowering Plants. 



To appreciate the evidence that certain forms of Viola are hybrids, 

 one should have some definite knowledge of the usual behavior of 

 known hybrids in other genera. This is well set forth in Focke's 

 great work,* which contains a compendious account of the two or 

 three thousand artificial and natural hybrids known at the time of 

 publication, and discusses the general laws governing this group of 

 phenomena. In regard to hybrids between nearly related but distinct 

 species their behavior as a rule may be stated as follows : — 



1. The hybrids have characters that are intermediate between the 



unlike characters of the parent forms. 



2. They and their offspring are stable ; that is, the several individuals 



resemble each other as closely as those that result from normal 

 sexual reproduction. 



3. They are more or less infertile, usually from defective pollen. 



4. They are unusually vigorous in their vegetative functions ; their 



flowers also are larger and remain longer in bloom. 



These four laws precisely describe the behavior of the hybrids 

 between any two well-marked species of our blue stemless violets. 

 If one parent is jjubescent and the other glabrous, the hybrid will be 

 somewhat pubescent ; if the cleistogamous peduncle in one is long 

 and erect, and in the other short and deflexed, it will be of medium 

 length and ascending in the hybrid; if the cleistogamous capsule is 

 green in one parent and purjile in the other, it will as a rule be green 

 but more or less flecked with purple in the hybrid. Furthermore, 

 the hybrids and their progeny are fairly constant. Thirty seedlings 



> Die Pflanzeii-MischliiiKe von W. O. Focke, Berlin, 1881. Octavo, 570 pages; no 

 English translation. 



