IRISH GARDENING 



VOLUME IX 



No. 96 



Edited by C- F. Ball. 



A MONTHLY JOURNAL DEVOTED TO THE 



ADVANCEMENT OF HORTICULTURE AND 



ARBORICULTURE IN IRELAND 



FEBRUARY 



1914 



Mendelism* 



By Professor James Wilson, M.A 



For the ])reeder of plants there has been no 

 more important discovery than that made half 

 a century ago by Gregor Mendel, the abbot of 

 Brunn : for it explains why plants are or aie not 

 like their parents, and so becomes a guiding 

 principle to breeders whether they woidd main- 

 tain their stock at its present level or alter or 

 improve it in one direction or another. 



Till Mendel's Mork was discovered and its 

 importance imderstood, some thirteen years ago, 

 the producer of new varieties had only two 

 methods of operation at his command. He 

 might search the globe for something new or 

 strange, or he might cross the varieties already 

 in his possession in a haphazard kind of way in 

 the hope that something unusual might emerge 

 from among their descendants. Then when the 

 novelty was discovered the great trouble was to 

 preserve it and keep it pure. Mendels discovery 

 sets aside neither of these methods, but rather 

 emphasises the need for both. Above all, how- 

 ever, it makes the breeders work far more 

 precise, by j^ointing with some certainty to the 

 plants to be selected as i)arents and by indicating 

 how their descendants should be dealt with in 

 order that those worth kee])ing may be sorted 

 out. preserved and purified. 



It used to be believed that when tAvo varieties 

 were crossed their descendants split up capri- 

 ciously, in the second and subsequent genera- 

 tions, into an irregular array of many different 

 varieties. The hrst part of Mendels work was 

 to show that this is not so, but that, although 

 they do split up into many varieties, these 

 varieties are produced on a legular plan and in 

 mim])ers peife('tly detiiiite and clear. 



Befoie Mendels time a large amount of work 

 had been done in the hybridisation of plants ; 

 and Mendel, who was keenly interested in the 

 subject, and saw that no one had gone to the 

 trouble of counting the numbers of varieties 

 produced by the hybridising of two different 

 pai'ents, determined to undertake the woi'k. To 

 this end he set about selecting his parent plants 

 with e.xtraoi'dinaiv judgment and care. First of 

 all he laid down three lulcs to which they must 

 conform, viz. : — (1) They miist differ from each 

 other by characters which bred true. (2) Their 

 hybrids must be naturallj^ protected or readily 



protectable from strange })ollen during the 

 flowering period. (3) The hybrids and their 

 descendants must suffer no serious diminution 

 in fertility. 



He then decided that the plant Avhich ful- 

 filled these conditions best, and was also most 

 easily cultivated, was the ordinary edible pea ; 

 and, having purchased the seed of 34 varieties, 

 he grew these under his own observation for two 

 years before starting his experiments, in order 

 to see that they fulfilled the conditions laid down 

 and that they bred true. 



At the end of the two years only 22 of these 

 varieties Avere retained, the rest haA'ing been 

 discarded. Among these 22 A-arieties he found a 

 number diffeiing fiom the ethers in one or more 

 of their salient features. Home had round seeds, 

 some Avrinkled ; some had long stems, some 

 short ; and so on ; and he mated a niimber of 

 plants Avhich differed from each other as regards 

 these salient features. For instance, he made 

 60 cross-fertilizations between plants haA'ing 

 round seed and ])lants having wrinkled : some- 

 times using the one kind as the male ])arent and 

 sometimes the other. All the progeny had rouiul 

 seeds only ; none had Avrinkleil. Similar results 

 folloAved all the other crosses. The hybrid 

 progeny were ahvays like one ])arent only as 

 regards the features in which the tAvo ])arents 

 diffei'cd. 



Th.e follouiiig taltle gi\^es the feature borne 

 by the ])areirt i)lants and the feature borne by 

 the hybrid ])rogeny of each se])arate pair : — 



Bij the Parenls. 

 Rinmd set'd and wrinkled 

 Yellow albumen and jireen . 

 (irey seed-coat and white 

 Inflated j)od.s and eonsf ricted 

 (Jreeii unripe pods and yellow 

 Axial flowers and terminal 

 Stems from fi to 7 feet lontjand ffom 

 ? to l.i feet ...... 



Bi/ lilt' Progeni/. 

 Round seed. 

 Yellow albumen. 

 Grey seed-coat. 

 Inflated pods. 

 (Jreeii uin-ipe j)ods. 

 Axial flowers. 

 Stems () to 7 fi'ct 



lonK. 



In connection Avith this phenomenon of a 

 feature — or chamder. as he called it — of one 

 parent being retnined Avhile the complementary 

 feature of the other ])arent is lost in the ])rogeny, 

 Meiulel used tAvo words a\ hich it is necessary to 

 remember. He called the feature Avhich is re- 

 tained the dominant and the one which is lost 

 the recessive. 



