I VI U"I>! ( HON. 



two species whoM flowers are of different sixe, those of 

 the hybrid are frequently of the nine tiw or approxi- 

 mate the size of the bloom of the specie* having the 

 larger flowers. Kxamples of uncommonly large flowers 

 are seen in Dianlhus artnariut X D. tuperbut, Rubut 

 etrtiiu X R. bellartlii. hybrids of ROM gallifa. Begonia 

 boliiitnns and Itoloma tydaum. 



A high vegetative power is very common in hybrids, 

 an in \ymphaa. Rub us catiut, Nicotiana tuavtoleni X 

 .V. l'i!tima. Linaria ttriata X L. vulgorit and Polamo- 

 grtun. A grrator duration of life has been noted in con- 

 in with several hybrids of \ifotiana and Digitalis. 

 ised reaistance to cold has been noted especially 

 in \i'-"'t'ina tuavtoleiu X ff. tabacum latitt.; whib , :\ 

 the other hand, Salix viminalis X 8. purpurta is more 

 sensitive to cold than either parent specie*. 



Those facts point in part to an apparent lessened 

 vitality f hybrids in consequence of their abnormal mode 

 <>f production ; and in part in some instances to an extra- 

 ordinary vcpetative power. The cause of this last phe- 

 non, which is observed less frequently than lessened 

 vitality, has been in some degree only recently nnder- 

 N'oteworthy experiments of Knight, Lecoq, and 

 others have been published, but it baa been through the 

 painstaking researches of Charles Darwin that the ease 

 with which a cross between different individuals and 

 races of one and the same species is effected was first 

 clearly explained. The increase of the vegetative power 

 in hybrid* is clearly a phenomenon that closely corre- 

 sponds with the peculiar conditions of hybrid produc- 

 ti.-n. and needs not a special explanation. It was at first 

 thought that lessened fertility was compensated for by 

 illative luxuriance, an hypothesis that Gart- 

 ner has shown to be untenable, as is evident by the fact 

 that many of the most fertile hybrids (Purala, MirabOit) 

 arc also notable for the largest growth. 



4 . 1 ' ARTI AL OB COMPLETE STERILITY or HYBRIDS. 



Subnormal fertility of hybrids, especially as regards 

 r!i-- pollen, has long been recognized as one of the most 

 important criteria of hybrids. It seems, however, that 

 haracter like intermediatenem has been an almost 

 unbridled conception and hence greatly overvalued as a 

 distinguishing feature. Focke in his summary gives us 

 a wealth of facts in this connection : 



Km mi PBoroarrnm. 



Byhndt brtuvr* diflrmt tpreiti (Aotc M their anttirn 

 nuiller number of normal pollm yrain* and tmaUrr 

 wimber of normal etd tkan m plant* of pun dftctnt. 

 Fnqvmtly tttry product mtitkrr pollen nor trrd. In 

 kyoridt*alion Wfipon airly rrlatrd meet Iki* teeuManinf 

 of Ike power of ttmual reproduction it not pretent. The 

 /lower* of itrrilr or nearly ttmle Aybrub usually rtmmm 

 frrtk for tony time. 



No property <>f hybrids has attracted so much atten- 

 as the lessening of the ability of sexual reproduc- 

 tion. Kulreuter believes that this peculiarity permits 

 a sharp border-line to be drawn between species and 

 varieties. Since then many botanists have accepted the 

 same view, and lately B. Naudin, Decaisne, and Caspary 

 have adopted it in a more or less modified form. Knight 

 and Klotzsch, and before them Godron, hold that the 

 p<>l!en of hybrids is entirely impotent, which contention 



had already been disproved by Kolreuter's accurate re- 

 searches. Kolreutrr is accredited with the promulga- 

 tion of the doctrine of complete sterility of hybrid*, but 

 tin* erroneous charge is to be explained only through 

 .in ignorance or misunderstanding of the Latin texts: 

 K.. In-lit, -r doea not speak of complete sterility, but only 

 of a lessened fertility, as a universal property of hybrids. 



In different plant genera the fertility of hybrids is 

 very varied. l-Vrtility is observed in a very low degree 

 in the hybrids Papavtr, Viola, Vtrbtucum, and Digitalis; 

 it is more common in Antmone, Nifolinnn. UtnlHa. 

 < 'rinum, Cucurbitacta, and I'tutifloraftn ; and it is more 

 common than sterility in Aquileyia, Dianthiu, Pelargo- 

 nium, drum. Epilobium. Ftuchia, Cotylfdon, lirgonia. 

 Cirrium, Erica. Rhododendron, Calrrolaria, Quercvi, 

 SaJtr, Gladiolus, Cypripedium, and Uipptattrum. In 

 the genera YH\, I'rtinus, Fngana. and P\rv, hybrids of 

 closely related species are used as seed-bearing plants; 

 and in Cereva the hybrids of widely separated species 

 show undiminitshed fertility. 



The sterility of hybrids is expressed at times by their 

 showing no inclination to flower, whirh peculiarity has 

 been noticed especially in several hybrids of Rhododen- 

 dron, Epilobium, Certvt, and Hymrnoralli*; but these 

 are exceptions, inasmuch as hybrids usually flower more 

 abundantly and earlier than true species. 



In hybrids with unisexual flowers the male flowers 

 fall off when in the bud, as in CuturbHarta and Hr- 

 gonia (hybrids of B. fnrbeli A. DC.). In bisexual flowers 

 the stamens are stunted, as noted in several hybrids of 

 Pelargonium and Digital** (D. lutea X !> pwpurra f. 

 tubi flora Lindl.). The most common sequel of hybrid 

 production is a deficient development of the pollen-grains 

 in hybrid plants. Commonly the anthers of hybrids are 

 sterile and do not contain any pollen ; or they arc 

 small and do not open. Such deficiency of pollen is 

 noted in Rubvu idtnu X R- odoniut. Ribft avrcum X 

 R. tanguineum, and Alopecunt* genirulatiu X A. pro- 

 tensit. In other caws the stamens produce small pow- 

 dery grains which do not swell with moisture, which are 

 of varying size and shape, and with which are usually 

 mixed a few single, well-formed, embryo-forming pollen 

 grains. The number of normal grains is, however, fre- 

 quently larger, and comprises 10, 20, or more per cent 

 of the total number. Large, rough grains which swell 

 with moisture, together with small well-formed grains, 

 are present often in greater or leas number among the 

 stunted grains. In hybrids of closely related species, as 

 in Melandryvm album X if. rubrum, but little irregu- 

 larity is usually found in the form of the pollen-grains. 

 In one hybrid, Sinningia, the pollen was better in the 

 second year of flowering than in the first 



In the hybrids of unquestionably different species a 

 normal formation of the stamens is seldom met with. 

 Assertions in support of this still need confirmation, in 

 part, therefore I refer to Nymphan Mut X N. rubn, 

 Btgonia rubrovrnia X B. ranthina, Itoloma tydarum X 

 /. tciadocalyx X Salve purpurta X 8. repent; pollen 

 grains which are all of nearly the same form are found 

 in Salix aunt a, and 8. caprea and 8. viminalit X 8. 

 repent. 



On the other hand, a deficient development of stamens 

 appears less frequently in race crossings. Possibly, fur- 



