A FORTNIGHTLY REVIEW ''"^^^^ 



BOTANICAI 



IMPERIAL DEPARTMENT OF AGRICULTURE FOR THE WEST INDIES, oardbn. 



Vol. VIII. No. ITS. 



B.\1;B.\D0S, FKliRUAPvY 20, 1909. 



PlUCK Id.. 



Mendelism 



PART II. 



■•" animals are transmitte' 

 ne.xt was described. 



X the editorial of the lust issue the system 

 according to \s-hich it has been shown that 

 simple ' unit characters ' in plants and 

 from one generation to the 



DC 



The cases of crjseinv dealt with in the previous 

 article were of the most simple nature only, i.e., those 



in which the individiuils concerned ditt'-ici Irom each 

 other in respect to but a single pair of characters. 

 More ftequeiitly, howevei', it will be found that the 

 original parents vary in a number of qualities, so that 

 the question becomes one of greater comple.xit}'. But 

 it has been shown that in gticti cases, each pair of 

 characters in whicii the parent plants (or animals,)' 

 differ is transmitted according to simple Mendelian. 

 rule, anil often independently of any other pair. 



To take an example : Tallness and dwarfness are 

 Mendelian characters in ordinary garden pea plants, 

 the former being dominant. Similarly, in the same 

 plant, as already mentioned, coloured flowers are domi- 

 nant to white flowers. We have here an example of 

 two pairs of unit qualities in the individuals to be 

 crossed. If now a t.ill pea plant having white flowers- 

 is crossed with a dwarf plant possessing coloured 

 blossoms, the plants of the next generation will all' 

 be tall, and will all bear coloured flowers. In the 

 offspiing of these hybrids, however, according to 

 Mendelian rule, both tall and short plants will 

 appear, the former being three times as numerous 

 as the latter. Out of every sixteen plants of the second 

 generation, therefore, twelve will be tall and four dwarf,. 

 The characters of colour and of whiteness in the flowers 

 are transmitted in a similar way, but quite independ- 

 ently of those of tallness and shortness, and distributed 

 equally among both the tall and the short plants, so that 

 there will be three with coloured blooms to one with 

 white among the ' tails,' and similarly three with 

 coloured blooms to one with white among the ' dwarfs. 



It will be seen that, as the result of crossing, 

 a combination of characters has been brought about, 

 and two new kinds of peas now e.xist, viz., coloured 

 tails and white dwarfs. In this generation, too, 

 a certain definite projiortion of each of the four classes 



