INTRODUCTION. 



15 



ttum and Musci. in which the production of sexual 

 spores i a n< i* the jinxluction of ]>>llen grams 



in the hvl.nds <-f Aerogamn. The obstacle to the regular 

 propagation of hybrids appears consequently to lie in the 

 nt of thi** individual cell* which have the 

 power to propagate the tyj>e of the parent form, and theie 

 particular cell* may or may not have the power of sexual 

 reproduction. At all events, more evidence must be 

 gathered before such a conception of a proposition of 

 MK h great biological importance is justifiable. As an 

 hypothesis thin gives no explanation, but it may prepare 

 the way fur tin- understandng of the conditions already 

 I, since it unites under one heading a number of 

 differ manifestly analogous phenomena in the 



animal and vegetable kingdoms. 



FIFTH Paoroamo.x. 



tlnlformolion and odd formi, rtprrtally of thr floirrrt. orr in 

 plniti muck mart common then in tpeciment of 



of pun mr**t. A* in Ppvr. DUathui, P*l.r 

 Itonium. Nicotian*, Idpiuli.. dntihl* flowrn alto appear 

 to h* produced with especial e*M in hybrid*. 



The Descendants of Hybrids. Hybrid planta are 

 more easily and more successfully fertilized by the pol- 

 :' the parent species than by their own pollen. Ex- 

 ceptions to this rule are rarely seen (as for instance in 

 -lum echioides X // aurantiacum), bat sufficient 

 .Mient* in this direction have not yet been made. 

 By their own pollen is understood the pollen of hybrids 

 resulting from the crossing of the same species, and not 

 only that of the identical specimens themselves. If hy- 

 tirul plants grow in the neighborhood of their parent 

 * they must frequently be fertilized by these spe- 

 and in this case many intermediate forms between 

 the hv'.nd and the parents will appear in their progeny. 

 It has never been determined whether or not fertilization 

 of the parents could take place by the pollen of the hy- 

 brid. The common statement, that the progeny of a 

 hylind are very variable, is therefore of bat little value. 

 Occasionally also a hybrid is more easily fertilized by the 

 pollen of a third species than by its own as in Nicotiana 

 rustic* X X. paniculata and Linaria purpurea X // 

 genixttrfotia. 



f'rogeny of Hybrids Fertilized by their Own Pollen. 

 (A X B) X (A X B) & . (1 ) If fertile hybrids are 

 protected from pollenization by the parent plants or by 

 plants of a different species, one will obtain hybrid 

 plants of a second generation. It is my opinion that the 

 progeny of hybrids exhibit marked differences in the 

 duration of life. In long-lived plants the blending and 

 mion of the two types united in the hybrid is 

 frequently more complete, so that the progeny inherit 

 the characteristics of this new intermediate type. The 

 progeny of annual or biennial hybrid plants are, as a 

 nile. particularly variable and rich in different forms, as 

 in Pimm, Phasrolu*. Lactufa, Tragopogon, Datura, A'tro- 

 tiana aJala X ff. langtdorffii, and so forth. Exceptions 

 are found in Brattica, Oenothera, Nicotiana nutica X 

 .V. panifulata, and Verbasntm austriacum X V. nigrum. 

 The progeny of perennial plants behave in general in 

 a similar way, bat the instances in which the interme- 

 diate type remains constant appear to be the more fre- 

 quent. Many of the hybrids often breed, moderately, 

 true, as in Aquilegia. Dianthut, I^aratera. Geum. Cerevf, 

 Begonia. Cirnium, Ffitracium, Primula, Linara, Veronica, 



l.amium. and Hipptattrum. The progeny of hybrid 

 shrub* and trees arc in the majority of cases moderately 

 .-table, as in JStculus. Amygdalut, Prwut. Srica, Qwr- 

 cut, and Salix; the progeny of many Futckia and <'al- 

 ctolaria are constant Some Rhododendron hybrids 

 breed true and a portion variably. The progeny of the 

 hybrids of Vitit, Pinu. and Cniayut appear to be very 

 variable. 



2. The different forms in which many primary hy- 

 brids appear are usually not stable in their offspring. 

 In Dianthui the leas-frequent forms ("Aosnahmetypen, 

 according to Gartner) usually revert to the normal hybrid 

 form. Mendel found that the different primary forms 

 of the Hieracium hybrids breed true. 



3. C. F. r. Gartner and other botanists have advanced 

 the proposition that the progeny of hybrids become 

 weaker and less fertile from generation to generation. 

 It is true that their vegetative power, which at first 

 is increased, is progressively decreased by self-fertiliza- 

 tion. Gartner's researches were, moreover, instituted on 

 a very small scale, so that not only very close inbreeding 

 bat also the many circumstances which cause deteriora- 

 tion in garden-plants of which only a few specimens are 

 cultivated influenced his hybrids. Gartner himself no- 

 ticed exceptions in Aquilegia, Dianthu* barbatut X D. 

 chinenu, and D. armeria. X D. deltoide*. Hybrids of 

 nearly related species are often grown perenially with 

 ease, as in Brastiro. ileJandryum, Mediengo, Petunia. 

 Many gardeners assert with great positiveness that many 

 hybrids can be propagated by means of seeds through 

 many generations, as in Lychni*. Erica, Primula aurimln 

 X P. nirtuta, and Datura.* Many observations on wild 

 plants seem to confirm these views. The theory has also 

 been advanced that the fertility of hybrids is increased 

 in later generations. It does not appear that such a rule 

 can have a universal validity. It is much nearer the 

 truth that many times fertile hybrids appear and that 

 they can easily increase under favorable environment 

 because of increased fertility. Fertile offspring of hy- 

 brids are, in fact, often products of back-crossings. 



4. Complete reversions to the parent forms without 

 influence of the parental pollen arise, except in rare in- 

 stances, only in hybrids of nearly related races. In such 

 hybrids true reversion appears only in a small number 

 of plants, as in Phateolut. 



5. From the variable progeny of fertile hybrids aer- 

 eral dominant types are often produced in three to four 

 generations. If these new types are protected from 

 crossing they tend to become constant. Scientific re- 

 searches which confirm these statements have been carried 

 out in bat small numbers, especially by Lecoq in ilira- 

 bilii, by Godron in Linaria and particularly in Datura. 

 Gardeners have produced many new races with well- 

 marked characteristics by crossing different species, and 

 many permanent wild intermediate forms have probably 

 originated in this way, as for example, Rraxsira, Lyhnu. 

 Zinnia, Primula, Petunia. Xicotiana rommutata. Pent- 

 ttemon, Mentha, and Lamium. The new type* of hybrid 

 progeny depart frequently in individual properties from 



"BoUakte ir U>l ipMio* o pnxhMwT (i. .. hybrid*) "rartrt 

 to mttttr ot UMir parraU IB the third or fourth tntntiem. or 

 bMOOM torfl* altocrtlMr. Thk < pUnibU ooocfc in theory, b) 

 U doMt. bat will not do in Ib* pottfcw \ 

 by Loudon. Arbrit H. p 944. 



