Discontinuous Variation occurring in Biscutella laevigata. 11 



acidity of the upper parts of the canal favours, in health at least, the 

 growth of the acid-forming bacteria, and may thus lead to an in- 

 creased acidity and diminished decomposition in the lower parts of 

 the canal. 



5. Some antiseptic substances appear to act more on the first class 

 of organisms than on the second. Thus salol seemed to act more 

 energetically on the liquefying forms than on the acid-forming class, 

 calomel the converse ; while salol exerted a greater antiseptic power 

 in the lower part of the intestinal canal, calomel in the upper 

 portions. 



6. Trypsin is capable of energetic proteolytic action in the presence 

 of organic acids, but, as it is slowly destroyed by these acids, it has 

 to be constantly supplied in fresh quantities. 



7. The figures obtained for the total solids of the different sections 

 show that absorption of fluids is greatest in the duodenum and 

 lower ileum. The absorption from the large intestine can not be 

 compared with the absorption from the other parts owing to the 

 number of times its contents represented the material newly passed 

 from the ileum. 



61 On a Discontinuous Variation occurring in Biscutella laevigata" 

 By E. R. Saunders, Lecturer of Newnham College, 

 Cambridge. Communicated by W. Bateson, F.R.S. Re- 

 ceived June 9, — Read June 17, 1897. 



The observations recorded in this paper were made upon Biscutella 

 laevigata, a cruciferous plant occurring as a perennial herb in the 

 alpine and sub-alpine regions of middle and southern Europe. It 

 was observed by Mr. Bateson that in a valley of the Italian Alps this 

 species exhibits two distinct forms,* which exist side by side, the one 

 hairy and the other glabrous. Plants showing various degrees of 

 hairiness, and constituting a series of intermediate forms connecting 

 the two extremes, were also found, but were comparatively scarce. 

 As it may be presumed that in the state of nature the two varieties 

 intercross freely, the question arises — how is their distinctness 

 maintained ? For on the supposition that hairiness and smoothness 

 are characters capable of blending freely, it might be expected that 

 offspring derived from a cross between hairy and smooth parents 

 would tend constantly to regress to a mean condition of texture. 

 It was in order to test the validity of this supposition, and to ascer- 



* Mr. Bateson's attention was drawn to the variations of this species whilst 

 staying in the Val Formazza, for the purpose of studying the alpine forms of the 

 butterfly Pieris napi, for it is upon these plants that the variety hryonice chiefly 

 lays its eggs in this locality. 



