in Hybridisation 337 ^ 



The experimental plants must necessarily — 



1. Possess constant differentiating characters. 



2. The hybrids of such plants must, during the flower- 

 ing period, be protected from the influence of all foreign 

 pollen, or be easily capable of such protection. 



3>, The hybrids and their offspring should suffer no marked 

 disturbance in their fertility in the successive generations. 



Accidental impregnation by foreign poLb n. if it occurred 

 during the experiments and were not recognized, would 

 lead to entirely erroneous conclusions. Reduced fer tility:, 

 or^rnti rn ntor il ity of rerf ain form s, ^^i^^h aq nrmrg in the . 

 Qfihpring of man y hy bri ds, would render the experime nts,^ 

 very difficult or entirely frustrate them. In order to dis- 

 cover the relations in which the hybrid forms stand towards 

 each other and also towards their progenitors it appears to 

 be necessary that all members of the series developed in 

 each successive generation should be, without exception, 

 subjected to observation. 



At the very outset special attention was devoted to the 

 Leguminosae on account of their peculiar floral structure. 

 Experiments which were made with several members of 

 this family led to the result that the genus Pisum was 

 found to possess the necessary qualifications. 



Some thoroughly distinct forms of this genus possess 

 characters which are rnrig:t-^pt-, and ea sily and certainly 

 reco p-nizable. and when their hybrids are mutually crossed 

 tTiey yield j^^l^^til y fertile progeny. Furthermore, a dis- 

 trn4)anre through foreign pnllen nnn nt easil y ocru rj since 

 tTie ferHhsing Organs are rlrsHy parked inc;ide_t he keel . 

 ar>d_j-Vip ani-Vipr bnrsts_ within the_ bud . SO that the stigma. 

 becomes covered_:adth--po11en even before the .flower opens. 

 This circumstance is of especial importance. As additional 

 advantages worth mentioning, there may be cited the easy 

 cultur e of thes e_j[ 3lants in the ope n ground and in ^ lot^r 

 and also their r elatively^^ shor t period of gt i o wth. ArtifidaL- 

 fertijisat inn i s rertRii i Ly a somew h at elaborate proce ^ but 

 nearly always succeeds. For this purpose the bnr| iq . 

 o^ene d^ before it is perfect ly developed, the keeHsjiefaevedr 

 a nd each stamen carei iill^ ^ G}araetcd by nicanG -of— ibr^eps. 

 after— wKirh_ the ^<-igm a can at once b^ -jdastedr over with--^ 

 t he foreign polje n^ 



B. H. 22 



