IVIKOM <T|m\. 



i; 



•. Rhodod* ad n i ii . A i in 111 1 in.-., i 'all cuhirin, i 

 and Hippeastrum) gardener have cro sed the 

 intentionally and unintentionally in the greatest variety 

 of ways, and from the forms obtained thej bave 

 those mo I desirable for further cultivation. The off- 

 spring of these complicated hybridization prodn 

 naturally almosl always very varied. On the other hand, 

 are ale. Sweel pari icularly 



emphasizes the fact thai the same bybrid form is obtained 

 from the ci 5 of several 1 omplex /'< m h\ - 



brids. Such constant complex Pelargonium hybrids are, 

 according to him, P. involucratum X P. ignescens, and 

 P. moslynce \ J', ignescens. It has already been 

 tioned thai Erica and several Salix hybrids on cro 

 furnish offspring of constanl form. 



Cross-breeds and Hybrids. — According to a dictum 

 h\ brids of two di Hi renl variet ies of one spe< ies 



I as cross-breeds, and hybrids of two different sp 

 as hybrids. As the term varieties 1- vague it is necessary 

 at this point to remember that only varieties which 

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

 tainty transmit in some degree their properties. I n- 

 stable breeds which are designated varieties are useless 

 ady of hybridization. 



Many writers have taken great pains to discov 

 sharp distinction between cross-bn eds and hybrids. They 

 hold to the expectation that by researches in hybridiza- 

 tion a border line between species and subspecies will be 

 fixed. Gartner, who in many places in his works has 

 declared that the conditions of the hybrids demonstrate 

 clearly the specific differences or similarities of the 

 parent-forms, would sunn retract, if he attempted to de- 

 velop any connection or continuity by the literature of 

 variety hybrids. Herbert and Naudin have through 

 many researches arrived at the conviction that it is im- 



ble to draw a sharp borderline between crosse 

 hybrids; nevertheless, later botanists have always sought 

 -ie h a fixed difference. 



The following propositions have been formulated: 



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



more or less numerous deformed pollen grains in a 

 hybrid. 



2. The fertility of a i ross breed 1- normal ; that of a 

 hybrid is distinctly sul 'mal. 



3. Hybrids of two spei es having d v 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. 



I. Cross have a decided inclination in later 



generations to revert entirely to the parent forms. 



These four propositions are in general correct, hut 

 give very little help to a final decision in doubtful 

 The hybrids of the red and arvensis must 



according to the pollen he considered a hybrid, but 



to the production of bii 

 breed. Datura hybrids, which are manifestly character- 

 istic hybrids in other ways, readily revert completely to 



rtility is apparently 



in no way weakened have already !>■ ified. The 



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



nearly rel - usually show the properties attrib- 



2 



uted to cro68-breeds, bul iblish 



a .-harp houndary line 

 rids. 

 era! oth it ies of ci ave been 



added by which they may be distinguished from 

 hybrids. Gartner has maintain 



tu 

 the first generation, while hybrids of i 

 will be of the same form. This assertion, which ha 



ntirely unjustified. The multi- 

 plicity of forms of the species-hybrids of Al 



flora, II ii mi nun , and BO forth has ahead 



out and. on tl ther hand. 1 first 



ation are usually as similarly ! 

 brids. Again, it is often m I that thi 



of one and i : :.- same spei 



produce the same hybrid forms. G irtner 1 specially has 

 emphasized this alleged behavior of " varieties," although 

 he must have known that K bad already 1 



the transmission of flower-coloring in race- of Mira 

 Dianthus, and Verbascum, the flower-filling (Bliithen- 

 fullung) of Aquilegia and Dianthus, and the form and 

 leaf-shape of races of Nicotiana tabacum and Htftt 

 The white blooming Datura ferox and D. strammonium 

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

 race (var. bertolonii) of the sam forms a blue- 



flowered hybrid. Nymphaa lotus] N. rubra is diffi 

 from N. lotus - A -. It i- unquestionable 



properties of races and 50-calL I es which are 



hereditary in pure-breeding are also transmitted to their 

 hybrid offspring. It is self-evidenl that form- n 



'1 offspring behave in an unstable fashion will also 

 produce polymorphous hybrids and I 



-tics of varieties will entirely disappear in the 

 products of t lie hybridization of pure 



The facts in short are as follows: The nearer the 

 morphological and systematic relationships of the p 



does the procreative power of the hybrid 

 depart from the normal. The farther the parent forms 

 are from one another the more commonly is the fertility 

 of the hybrid weakened. Exceptions, however, an 

 infn quent. 



The nearer the parent forms are related to one an- 

 other, the more frequently does the offspring of hybrids 

 show reversion in the parent forms. 



Hybrids of nearly rel -how 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 - 



The most asymmetrically variegated (lowers (.Vi'ra- 

 bilis, Camellia, Mimulus, /' rnd so forth) have, 



moreover, I from the offspring of hybrids. 



Tim propositions of Fo< 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 ami addi- 

 tions of a more or less important character to the data 

 and propositions sel forth, but this 91 

 the purpi is chapter and tl rch. 



