ivii;>i)i i in .\ 



17 



! -Ictolana. Gladiolus, 



and // i/'/wojifrum ) gm .ave trussed the species 



intentionally anil unintentional!} rreatest variety 



of u.u-. .iii-l ftfiii tin* forms obtained they have used 



tho* -inMe for furthi-r cultivation. The off- 



j>m _ "f thew complicated hybridi/ation pr->dui-ts are 



naturally almost iilw.i-. - \er> \an|. On the other hand. 



ther> > t!n rule. Sweet particularly 



: that the same hybrid form is obtained 



frirtii -.-v.-ral i<>nipl> -\ /V/.ir./.iriiur/i In - 



l.ri.l- Such . ..MM.UI! complex I'rlargonium hybrid* are, 



im_- t him. /' i ; /'. ignrttetu, and 



/'. mnxii/mr /' P/I,. ,.. It ban already been men 



rica and several Salix hybrids on crowing 



fiirin-h i.if-j.r!!:.' of i onstant form. 



- nnil Hybrids. According to a dictum 

 hybrid* <>f two different varieties of one species are desig- 

 nated as cross-breeds, and hybrids of two different specie* 

 as hybrids. As the term rarieties is vague it is necessary 

 int to remember that only varieties which 

 breed true, as well as races, or subspecies, can with cer- 

 tainty transmit in some degree their properties. Un- 

 stable breeds which are designated varieties are useless 

 in the study of hybridization. 



Many writers have taken great pains to discover a 

 sharp '!;-tm. lion between cross-breeds and hybrids. They 

 the expectation that by researches in hybridiza- 

 i l-order lino between species and subspecies will be 

 rtniT. who in many places in his works has 

 rod that the conditions of the hybrids demonstrate 

 v the specific differences or similarities of the 

 t- forms, would soon retract if he attempted to de- 

 an v connection or continuity by the literature" of 

 variety hybrids. Herbert and Naudin have through 

 many researches arrived at the conviction that it is im- 

 possible to draw a sharp borderline between crosses and 

 yfcridi : nevertheless, later botanists have always sought 



i lived difference. 



Thi> following propositions have been formulated: 

 1 . The pollen of a cross-breed is normal ; there are 

 or less numerous deformed pollen grains in a 

 hybrid. 



The fertility of a cross-breed is normal ; that of a 

 hybrid is distinctly subnormal. 



3. Hybrids of two species having differently colored 

 flowers hear flowers of modified coloring. Plants with 

 irregularly dappled flowers are produced from the cross- 

 ing of varieties. They behave similarly in regard to 

 coloring, marking, and formation of fruit, and other 

 properties. 



4. Cross-breeds have a decided inclination in later 

 generations to revert entirely to the parent forms. 



The> four propositions are in general correct, but 

 give very little help to a final decision in doubtful cases. 

 The hybrids of the red and blue Anagallit arvensis must 

 according to the pollen be considered a hybrid, but 

 according to the production of bicolored flowers, a cross- 

 breed. Datum hybrids, which are manifestly character- 

 vbrids in other ways, readily revert completely to 

 the parent species. Hybrids whose fertility is apparently 

 in no way weakened have already been specified. The 

 rule can. therefore, be set forth that hybrids of very 

 nearly related races nsuallv show the properties attrib- 

 2 



* and 



ut. d to cross-breeds, but it is another matter I 

 a sharp boundary line between race-cross-b 

 species-hybrid*. 



Several other properties of cross-breeds ban boon 

 added by hirl, they may be distinguished from spodoa- 

 !i\l-ndv <. .rtn.-r has maintained that i- rods-breeds of 

 a similar origin will IK- very unlike one another even m 

 tin- first generation, while hybrid* of the first generation 

 will be of the same form. This assertion, which has been 

 repeated by others, is entirely unjustified. The multi 

 plicity of forms of the species-hybrids of AbulUnn. I'atsi- 

 flon, Hirracium, and so forth ha* already been pointed 

 out and, on the other hand, race-cnxw-breeds of the first 

 generation are usually as similarly formed as true hy- 

 brids. Again, it is often maintained that the var 

 <>f one ami the same species if croesed with another species 

 produce the same hybrid forms. (I.irtin-r csjiecially has 

 emphasized this alleged behavior of " varieties," although 

 he must have known that Kn! renter had already 

 the transmission of flower-coloring in races of Mirabilis. 

 Dianthus, and Vrrbascum, the flower-filling (Rliithen- 

 fullung) of AquUegia and Dianthus, and the form and 

 leaf-shape of races of Nicotiana taborum and Hibiscus. 

 The white-blooming Datum frror and /). strtunmonium 

 typ. (a white-flowered form) with the smooth-fruited 

 race (var. bertolonii) of the same specie* forms a blue- 

 flowered hybrid, ffymplxra loiux X N. rubtu is different 

 from N. lotus X N. denlata. It i* unquestionable that 

 properties of races and so-called varieties which are 

 hereditary in pure-breeding are also transmitted to their 

 hybrid offspring. It is self-evident that forms whose 

 normal offspring behave in an unstable fashion will also 

 produce polymorphous hybrids and that the unstable 

 characteristics of varieties will entirely disappear in the 

 products of the hybridization of pure species. 



The facts in short are as follows: The nearer the 

 morphological and systematic relationships of the parent 

 forms the loss does the procreative power of tin- hyl>nd 

 depart from the normal. The further the parent form* 

 are from one another the more commonly is the fertility 

 of the hybrid weakened. Exceptions, however, are not 

 infrequent. 



The nearer the parent forms are related to one an- 

 other, the more frequently does the offspring of hybrids 

 show reversion to the parent forms. 



Hybrids of nearly related parent-forms show in their 

 fruits the characteristic properties of the parents un- 

 blended and side by side, but in hybrids of very different 

 parent forms this is seldom seen. 



The roost asymmetrically variegated flowers (Jfiro- 

 bi'/i*, Camrllin, Mimttlu*, Petunia and so forth) ' 

 moreover, originated from the offspring of hybrids. 



Tho propositions of Focke, although published in 

 1881, are not subject to modifications in principles 

 even at the present time. Much literature on the sub- 

 ject of the sterility of hybrids might be quoted and 

 some references might be made to extensions and addi- 

 tions of a more or lest important character to the data 

 and propositions set forth, but this seems needless for 

 the purposes of this chapter and this research. 



