A. H. Trow 



167 



There appears to be a distinct impediment to the production of green- 

 stemmed, non-radiate plants, and therefore a tendency to the formation 

 of a 9 ; 3 : 4 ratio. 



The examination of the F3 generation of the cross lanuginosus 

 X midticaiilis for stem cohnir was attended with difficulties. It is 

 diflScult to arrange the plants under the three types GG, Gg and gg, 

 owing possibly to the direct colour modifications due to the environ- 

 ment. Much more work is required before a clear and complete 

 explanation can be given of the results in the case of this cross. 

 Six colonies were examined, all growing together in the open air, 

 under conditions as similar as possible. The outside plants of each 

 colony might have been expected to shew differences when compared 

 with the inside ones, but none were noticed, although specially looked 

 for. On the other hand, a certain effect of shading was very obvious; 

 when the earlier plants were uprooted for examination from some of 

 the beds, the later ones received considerably more light and air, and 

 their stems quickly acquired a certain amount of red colouring matter. 

 This kind of response is well known to botanists, and appears to be 

 more or less independent of the colour factors for stems that we are 

 considering here. Tiie result of the examination of these six colonies 

 for stem colour is presented in 



TABLE XVIII. 



It does not seem desirable to spend much time in analysing further 

 these incomplete results. Additional experiments are necessary. Never- 

 theless all are of interest. Green is apparently recessive. It is certainly 

 easier to pick out the pure greens (gg), for the pure reds are apt to pass 

 over more or less gradually into the reddish greens. 



