IRISH GARDENING 



VOLUME IX 

 No. gS 



Edited by C- F. Ball. 



A MONTHLY JOURNAL DEVOTED TO THE 



ADVANCEMENT OF HORTICULTURE AND 



ARBORICULTURE IN IRELAND 



Al'RIL 

 1914 



Mendelism* 



third paper. 

 By Professor James Wilson, M.A. 



In last month's Irish Gardening we finished 

 up with an abbreviated statement of the crucial 

 observations which Mendel made regarding the 

 phenomena re- 

 corded in his 

 experiments, and 

 stated at the 

 same time the 

 theory which he 

 propounded to 

 account for those 

 phenomena. It 

 may be well to 

 recapitulate : 

 putting the ob- 

 s e r V a t i o n s i n 

 ordinary type 

 and the theory 

 in italics : — 



i. Pure species 

 })roduce pure- 

 breeding forms. 



They must be 

 furnished, there- 

 fore, with the 

 materials for 

 doing so. 



ii. Hybrids also 

 produce pure- 

 breeding forms. 



Therefore, theij 

 alao must be fur- 

 nished with the materials for doing so. 



iii. Hybrids produce equal numbers of pure- 

 breeding individuals in every type they produce. 



Therefore, they must be furnished ivith equal 

 numbers of the materials to produce their jmre- 

 breeding jjrogeny. 



The crucial stateinent is that liybrids must he 

 furnished with equal numb(>rs of materials. 

 Mendel merely remarked that this could 1k' 

 proved theoretically — that is, from the know- 

 ledge already accumulated— and went on to 

 prove it experimentally. It will be worth while 

 to see hott- it can be proved theoretically. 



If Mendel's theory he tine, tlie hybrids 

 ])etween round and wrinkh d peas should be 

 giving off equal numbers of the materials to 



produce roinid- 

 ness and wrink- 

 ledness. We can 

 represent one of 

 them as doing so, 

 thus :— 



In the pollen : 



in the ovarv 



Saxifkaga Kochemana. 



R 



M- 



The materials for 

 roiuidness in the 

 ])ollen have etiual 

 chances of mating 

 with either those 

 for roundness or 

 those for wiink- 

 ledness in the 

 ovary. 



The materials 

 for wrinkledness 

 in the pollen have 

 also e([ual chances 

 of mating with 

 those for round- 

 ness or wrinkled- 

 ness in the ovary. But, as the materials foj- 

 roiuidness oi- Mrinkledness in the poMen have 

 themselves e(|ual chances of mating Mith 

 materials of any kind in the ovaries, the 

 chances are e(|iial that the young plant i)ro- 

 duced ])y the mating of the materials in the 

 pollen with those in the ovary shall start off 

 with the materials IJiJ, or Bw, or wR, or ww. 

 The following iliagram may show this more 



clearlv : — 



^R 



X. 



w ^w 



Then, if a sufficient number of fertilizations 



