D. J. SCOURFTELD OX MENDELI8M AND MICROSCOPY. 403 



If the results from the above matings are tabulated it will be 

 found that nine distinct combinations are produced, and when the 

 effect of the dominance of R over W and Y over G is allowed for, 

 the outcome is found to be 9 RY + 3 RG + 3 WY + 1 WG, 

 a, result already shown to be confirmed by experiment. The effect 

 of back crossing with a recessive in both characters will Obviously 

 be exactly the same as shown by the fourth of the above sets of 

 combinations — i.e. there will be equal numbers of RY, RG, WY, 

 and WG. Mendel carried out this experiment among others, and 

 found that he did get, as anticipated, approximately equal 

 numbers of each of the four types. 



In addition to his experiments with peas, Mendel also worked 

 with beans, hawk weeds, and other plants. In the case of the 

 beans he found that all the characters selected for observation, 

 with the exception of colour, obeyed the same law as had been 

 found to hold good for peas, and to explain the peculiarities in the 

 inheritance of colour, he made the valuable suggestion that 

 possibly two or more pairs of characters were involved in pro- 

 ducing the naked-eye effect. This idea is most likely correct, and 

 it has been found to be certainly true in other cases. The hawk- 

 weeds, on the other hand, did not seem to lend support to the law 

 of gametic purity, but rather pointed to the existence of more 

 complicated law r s of inheritance. The experiments, however, were 

 on a small scale and very difficult to carry out, and the results 

 therefore not very convincing. 



Some thirty- five years after the above results were obtained, it 

 happened that a few botanists — e.g. De Yries, Correns, Tschermak, 

 Spillman, and others — were independently carrying out somewhat 

 similar experiments to those of Mendel, and getting practically 

 identical results. The rediscovery of his paper in 1900, therefore, 

 at once brought the subject into prominence, and thereby gave a 

 great impetus to experimental w T ork on heredity in general. 

 Since that year there has been a very large amount of work done 

 on the lines laid down by Mendel, and not only have his own 

 experiments been repeated and verified, but the law he formulated 

 has been found to apply to numerous characters other than those 

 he dealt with, and to animals as well as plants. 



On the botanical side may be mentioned such researches as 

 those of De Vries, on maize and many garden plants ; I lorrens, 

 on stocks and maize; Tschermak, on stocks andibeans; Bateson 



